So that the body in the elevator experiences an overload. It is very difficult or impossible to carry out many phenomena and experiments in the conditions of an educational institution. "The Formation and Propagation of Waves

1. As you already know, the force with which the body, due to its attraction to the Earth, acts on a support or suspension, is called body weight P.

The weight of the body is applied to a support or suspension; in contrast, gravity is applied to the body. Weight and gravity not only have different points of application, but also have different natures: gravity is a gravitational force, and weight is an elastic force.

From the 7th grade physics course, you also know that if a body suspended on a thread or placed on a support is at rest or moves uniformly and rectilinearly, then its weight is modulo equal to the force of gravity:

P = mg.

2. Let us now assume that the body, together with the support or suspension, moves relative to the Earth with acceleration. Will the weight of the body and the force of gravity be equal in this case?

Consider the movement of a person in an elevator. Let the elevator have acceleration a pointing down (Fig. 52). In the inertial reference system associated with the Earth, a person is affected by: gravity, directed downwards, and the elastic force from the side of the elevator floor, directed upwards. The elastic force in this case is called support reaction force and denoted by the letter N. The resultant of these forces imparts acceleration to a person.

Using Newton's second law, we can write in vector form:

F = ma,
F heavy + N = ma.

Let's direct the axis Y vertically down and write this equation in projections onto this axis, taking into account that F strand = mg, projections of acceleration and gravity on the axis Y are positive, and the projection of the support reaction force is negative. We get:

mg – N=ma.

From here:

N = mg – ma = m(g – a).

According to Newton's third law, the modulus of a body's weight is equal to the support reaction force:

P = N.

Then

P = m(g – a).

From the formula obtained, it can be seen that the weight of the body is less than the force of gravity. In this way, if a body, together with a support or suspension, moves downward with an acceleration that is directed in the same direction as the acceleration of free fall, then its weight is less than gravity, i.e., less than the weight of a body at rest.

The decrease in weight you experience while in the elevator, at the moment it begins to move down.

If the acceleration of the body is equal to the acceleration of free fall a = g, then the body weight P= 0. Such a state is called the state weightlessness. Astronauts are in a state of weightlessness spaceship during the flight, as they move around the Earth with a centripetal acceleration equal to the acceleration of free fall.

But not only astronauts experience a state of weightlessness. The runner may be in this state for short periods of time when both feet are off the ground; ski jumper during flight.

3. Consider again the movement of the elevator and the person standing in it. But only now the elevator has acceleration a pointing up (Fig. 53).

Using Newton's second law, we can write:

F = ma,
F heavy + N= ma.

guiding the axis Y vertically down, we write this equation in projections on this axis:

mg – N = -ma; N = mg + ma; N = m(g + a).

Insofar as P = N, then

P = m(g + a).

It can be seen from the formula that the weight in this case is greater than the force of gravity. In this way, if a body, together with a support or suspension, moves with an acceleration directed opposite to the acceleration of free fall, then its weight is greater than the force of gravity, i.e., greater than the weight of a body at rest.

The increase in body weight caused by movement with acceleration is called overload.

You experience an overload in the elevator, at the moment it starts moving up. Cosmonauts and pilots of jet planes experience enormous overloads during takeoff and landing; pilots performing on the plane aerobatics "dead loop" at its lowest point. In order to reduce the pressure on the skeleton of the astronauts during takeoff, special chairs were made in which the astronauts are in a semi-lying position. In this case, the pressure force that acts on the astronaut is distributed over a larger area, and the pressure on the skeleton becomes less than when the astronaut is in a sitting position.

4. Problem solution example

What is the weight of a pilot with a mass of 70 kg, performing a "dead loop" at the lower and upper points of the trajectory, if the radius of the loop is 200 m, and the speed of the aircraft when passing the loop is 100 m/s?

Given:

Solution

m= 70 kg

R= 200 m

v= 100 m/s

g= 10 m/s 2

The force of gravity acts on the pilot at the lower and upper points of the trajectory F gravity and reaction force from the seat N(Fig. 54). The reaction force of the support is equal in modulus to the weight of the pilot: P = N.

According to Newton's second law, we can write:

N + F heavy =ma.

P 1?

P 2?

For the lower point of the trajectory, this equation is in projections onto the axis Y(Fig. 54, but) will look like:

–N 1 + F heavy = - ma, or N 1 – mg= ma.

Consequently,

P 1 = N 1 = ma+ mg= m(a + g).

For the upper point of the trajectory (Fig. 54, b) can be written:

N 1 + F strand = ma.

From here

N 1 = ma – mg.

Consequently,

P 2 = N 1 = m(a – g).

Insofar as a= , then

P 1 = m + g; P 2 =– g.

P 1 \u003d 70 kg + 10 m / s 2 \u003d 4200 N;

P 2 \u003d 70 kg - 10 m / s 2 \u003d 2800 N.

If the force of gravity acting on the pilot F weight = 70 kg 10 m/s 2 = 700 N, then its weight at the lower point of the trajectory is 6 times greater than gravity: == 6. They say that the pilot experiences a sixfold overload.

At the top of the trajectory, the pilot experiences a fourfold overload: == 4.

Answer: P 1 = 4200 N; P 2 = 2800 N.

Questions for self-examination

1. What is body weight? What is the nature of body weight?

2. When is the weight of a body equal in magnitude to the force of gravity?

3. How does the weight of a body change when it moves with an upward acceleration; down?

4. What state is called the state of weightlessness? When does it come?

5. What is the overload condition? When is overload experienced?

Task 15

1. The elevator starts moving down with an acceleration of 2 m/s 2 . What is the weight of a 60 kg person standing in this elevator?

2. With what force does a car of mass 1 ton press on the middle of a convex bridge with a radius of curvature of 30 m? The speed of the car is 72 km/h.

3. A stone weighing 400 g is rotated uniformly in a vertical plane on a rope 1 m long at a speed of 2 m/s (Fig. 55). What is the tensile force of the rope when the stone passes the upper and lower points of the trajectory?

Option 1.

An airplane flies in a straight line at a constant speed at an altitude of 9 km. The frame of reference associated with the Earth is considered to be inertial. In this case:

1) there are no forces acting on the plane

2) the plane is not affected by gravity

3) the sum of all forces acting on the aircraft is zero

4) gravity is equal to the Archimedes force acting on the plane

A body of mass 1 kg is acted upon by forces of 6 N and 8 N, directed perpendicular to each other. What is the acceleration of the body?

1) 2 m/s 2 2) 5 m/s 2 3) 10 m/s 2 4) 14 m/s 2

satellite massT R

1) 2) 3) 4)

A 2 kg mass is hung from a spring 10 cm long with a stiffness coefficient of 500 N/m. What is the length of the spring?

1) 12 cm 2) 13 cm 3) 14 cm 4) 15 cm

A man was carrying a child on a sled along a horizontal road. Then a second similar child sat on the sled, but the man continued at the same constant speed. How did the force of friction change in this case?

A block slides down an inclined plane. Which vector shown in the figure is superfluous or incorrect?

1) 2) 3) 4)

2) on siteDE

3) on section AB the car moved uniformly

Part B

Three bodies of the same mass, 3 kg each, made movements. The displacement projection equations are presented in the table. Which graph shows the dependence of the projection of the force on time acting on each body?

Solve problems.

A body with a mass of 10 kg suspended from a cable rises vertically. With what acceleration does the body move if a cable with a stiffness of 59 kN/m is extended by 2 mm? What is the elastic force in the rope?

The average height of the satellite above the Earth's surface is 1700 km. Determine the speed of its movement.

Option2 .

Part A Choose one correct answer.

The movements of bodies relative to the Earth are listed below. Which frame of reference associated with one of these bodies cannot be considered inertial? The frame of reference associated with the Earth is considered to be inertial.

1) the girl runs at a constant speed

2) the car moves evenly on the horizontal part of the road

3) the train is moving uniformly

4) Hockey puck slides evenly on smooth ice

1) 2 m/s 2 2) 4 m/s 2 3) 1 m/s 2 4) 8 m/s 2

What expression determines the value of the first space velocity of the satellite, if the radius of the circular orbitR, and the free fall acceleration at this heightg?

1) 2) 3) 4)

In order for the body in the elevator to experience overload (weight gain), it is necessary:

1) accelerated movement of the elevator up

2) slow movement of the elevator up

3) accelerated movement of the elevator down

4) such a state is impossible

A man was carrying two identical children on a sled along a horizontal road. Then one child got up from the sled, but the man continued to move at the same constant speed. How did the force of friction change in this case?

1) did not change 2) doubled

3) decreased by 2 times 4) increased by 50%

1) 2) 3) 4)

The speed modulus of a car weighing 1000 kg changes in accordance with the graph shown in the figure. Which statement is true?

1) on the BC segment, the car was moving uniformly

2) in section CD

3) on siteDEthe car was moving with uniform acceleration, the acceleration vector coincides in direction with the velocity vector.

4) the acceleration module in section AB is less than the acceleration module in sectionDE

Part B

Using the condition of the problem, match the equations from the left column with their graphs in the right column.

Solve problems.

A bus weighing 15 tons starts off with an acceleration of 0.7 m/s 2 . What friction force acts on the bus if the engine traction force is 15 kN? Express the answer in kN. What is equal to the coefficient friction?

The average height of the satellite above the Earth's surface is 900 km. Determine the speed of its movement.

Option 3.

Part A Choose one correct answer.

A parachutist descends vertically at a constant speed of 2 m/s. The frame of reference associated with the Earth is considered to be inertial. In this case:

1) there are no forces acting on the parachute

2) gravity is balanced by the Archimedes force acting on the parachute

3) the sum of all forces acting on the parachute is zero

4) the sum of all forces is constant and not equal to zero

A body of mass 2 kg is acted upon by forces of 3 N and 4 N, directed perpendicular to each other. What is the acceleration of the body?

1) 3.5 m/s 2 2) 2.5 m/s 2 3) 7 m/s 2 4) 10 m/s 2

satellite massT moves around the planet in a circular orbit of radiusR. The mass of the planet M. What expression determines the value of the speed of the satellite?

1) 2) 3) 4)

The elevator is equipped with spring scales on which a person stands. How will the readings of the scales change when the elevator moves up and down at an accelerated rate?

1) up - increase, down - decrease

2) up - decrease, down - increase

3) up - increase, down - do not change

4) up - will not change, down - will increase

A man was carrying a child on a sled along a horizontal road. Then a second similar child sat on the sled, but the man continued at the same constant speed. How did the coefficient of friction change in this case?

1) did not change 2) doubled

3) decreased by 2 times 4) increased by 50%

A block moves upwards along an inclined plane with uniform acceleration. Which vector shown in the figure is superfluous or incorrect?

1) 2) 3) 4)

The speed modulus of a car weighing 1000 kg changes in accordance with the graph shown in the figure. Which statement is true?

1) on the BC segment, the car moved evenly

2) in section CDthe car was moving with uniform acceleration, the acceleration vector is directed opposite to the velocity vector

3) on siteEFcar rested

4) the acceleration module in section AB is less than the acceleration module in sectionDE

Part B

Using the condition of the problem, match the equations from the left column with their graphs in the right column.

Three bodies of the same mass, 4 kg each, made movements. The displacement projection equations are presented in the table. Which graph shows the dependence of the projection of the force on time acting on each body?

Solve problems.

The elevator descends with an acceleration of 2 m/s 2 . In an elevator, a load weighing 0.7 kg hangs on a spring with a stiffness of 560 N/m. What is the spring force? By how many centimeters did the spring lengthen?

The average height of the satellite above the Earth's surface is 600 km. Determine the speed of its movement.

Option4 .

Part A Choose one correct answer.

1) the elevator falls freely

2) the elevator rises evenly

3) the elevator moves slowly up

4) the elevator is moving rapidly down

Four forces act on a body of mass 2 kg. What is the acceleration of the body ifF 1 =12 H, F 2 =18 H, F 3 =20 H, F 4 =18 H.

1) 6 m/s 2 2) 16 m/s 2 3) 2 m/s 2 4) 4 m/s 2

The mass of the Moon is about 81 times less than the mass of the Earth. What is the ratio of the gravitational forceF 1 , acting from the side of the Earth to the Moon, to the forceF 2 acting from the side of the Moon to the Earth?

1)1/81 2) 81 3) 9 4) 1

How to make a 10 N weight stretch the dynamometer spring with a force greater than 10 N?

1) move the dynamometer with the weight down with some acceleration

2) move the dynamometer with the weight up with some acceleration

3) a dynamometer with a weight must fall freely

4) this is impossible to do

A man was carrying two identical children on a sled along a horizontal road. Then one child got up from the sled, but the man continued to move at the same constant speed. How to change the coefficient of friction in this case?

1) doubled 2) doubled

3) increased by 50% 4) did not change

A bar moves uniformly upward along an inclined plane. Which vector shown in the figure is superfluous or incorrect?

1) 2) 3) 4)

The speed modulus of a car weighing 1000 kg changes in accordance with the graph shown in the figure. Which statement is true?

1) in section CDthe car was moving with uniform acceleration, the acceleration vector coincides in direction with the velocity vector

2) the acceleration module in section AB is greater than the acceleration module in sectionDE

3) on siteDEthe car was moving with uniform acceleration, the acceleration vector is opposite to the velocity vector.

4) on section AB the car moved uniformly

Part B

Using the condition of the problem, match the equations from the left column with their graphs in the right column.

Three bodies of the same mass, 2 kg each, made movements. The displacement projection equations are presented in the table. Which graph shows the dependence of the projection of the force on time acting on each body?

Solve problems.

A car weighing 1 t moves with an acceleration of 0.8 m/s 2 . A force of 2 kN acts on the car? Determine the thrust force of the engine (express the answer in kN) and the coefficient of friction.

The average height of the satellite above the Earth's surface is 300 km. Determine the speed of its movement.

Task number 6

Question:

Two forces are applied to the body, the modules of which are 10 N and 20 N. It is known that the forces are directed along one straight line and in opposite directions. What will be the net force (in N)?

Write down the number:

________10 ________________

Task number 7

Question:

A body weighing 100 kg is affected by a resultant force equal to 20 N. What is the acceleration modulus of the body (in m / s 2)?

Write down the number:

_________0,2 _______________

Task number 8

Question:

A body of mass 5 kg rests on a horizontal surface of a table. Determine with what force (in N) the table will act on this body?

Write down the number:

__________49 _______________

Task number 9

Question:

The figure shows two forces acting on the body. Find the modulus of force F2(in N) if the body moves to the right with a constant speed of 2 m/s.

Image:

Write down the number:

________17,3 ________________

Task number 10

Question:

A body of mass m moves with an acceleration of 3 m/s 2 . How many times must the resultant force increase in order for the body to start moving with an acceleration of 9 m / s 2?

Write down the number:

______3_________________

The law of universal gravitation. space speeds

Task number 1

Question:

The coefficient of proportionality in the formula describing the law of universal gravitation is numerically equal to ...

1) Order 10 9

2) Order 10 5

3) Order 10 -19

4) Order 10 -11

Task number 2

Question:

Choose the quantities on which the first two cosmic velocities of this planet depend

Choose from 5 answer options:

Weight

2) Albedo

Radius

4) The period of revolution around its axis

5) The period of revolution around its star

Task number 3

Question:

Choose the correct statements

__ Gravitational interaction between bodies always manifests itself in the form of mutual attraction

__ The force of gravity is proportional to the masses of bodies

The force of gravity is inversely proportional to the distance between the bodies

The law of universal gravitation is universal and can be applied with high accuracy to any pair of bodies

Task number 4

Question:

The speed at which a body must move in order to leave the orbit of a given celestial body is ...

Choose one of 4 answer options:

1) The first cosmic velocity of a given body

2) The second cosmic velocity of a given body

The third cosmic velocity of a given body

4) The fourth space velocity of a given body

Task number 5

Question:

The pencil rests on the table. What kind of interaction is this?

Choose one of 4 answer options:

gravitational

2) Electromagnetic

3) Strong

Task number 6

Question:

Find the force (in mN) with which two asteroids are attracted to open space weighing 10,000 tons each, if the distance between them is 1 km.

Write down the number:

_______6,67 _________________

Task number 7

Question:

In order to make an aircraft an artificial satellite of a certain planet, this aircraft, taking off from this planet, needs to develop a speed of 2 km / s. If the mass of this planet is 1023 kg, then what is its radius (in km)?

Write down the number:

______1667,5 _________________

Task number 8

Question:

Find the second escape velocity of the moon in km/s. The mass of the Moon is 7.3x10 22 kg, and the radius is 1737 km.

Write down the number:

______1,67 _________________

Task number 9

Question:

Find the force (in TN) with which the Sun acts on Pluto. The mass of the Sun is 2x10 30 kg, the mass of Pluto is 1.3x10 22 kg. The average distance between the Sun and Pluto is taken equal to 5913 million km.

Write down the number:

_____49600 _________________

Task number 10

Question:

Find the radius of a planet (in km) whose first escape velocity is 12 km/s and whose free fall acceleration is 15 m/s 2 .

Write down the number:9600

The force of gravity. Weight, weightlessness, overload

Task number 1

Question:

Choose the correct statements

Indicate the truth or falsity of the answer options:

YES) The force of gravity acting on a body is equal to the product of the mass of the body and the acceleration of free fall

NO) The weight of the body is equal to the product of the mass of the body and the acceleration of free fall

NO) Weight is a scalar quantity

YES) Weight is the force acting on a support or suspension

Task number 2

Question:

A person experiences overload while in an elevator if...

Choose one of 4 answer options:

1) The elevator is at rest

The elevator goes up

3) The elevator goes down

4) If a person stands on his hands

Task number 3

Question:

Astronauts in Earth orbit experience weightlessness because...

1) They are far enough away from the Earth that gravity is no longer acting on them.

They are in free fall, falling around the earth

3) They begin to attract other celestial bodies, and the total action of these bodies balances the force of gravity acting from the Earth

Task number 4

Question:

Match the situation with the consequence of this situation.

Please indicate the correspondence for all 4 answer options:

The pilot is experiencing overload

2) The force of gravity acting on the pilot is not equal to his weight

3) The force of gravity acting on the pilot is equal to his weight

4) The pilot experiences weightlessness

4) The plane goes into a tailspin

The plane is coming out of a dive

3) The plane flies with horizontal acceleration

2) The plane flies with vertical acceleration

Task number 5

Question:

Is the Earth in a state of weightlessness?

Choose one of 3 answer options:

3) Depending on the choice of reference system

Task number 6

Question:

The waiter lifts the tray vertically upwards with an acceleration of 3 m/s 2 . The mass of the dish on the tray is 2 kg. Determine the force (in N) with which the utensil acts on the tray.

Write down the number:

____________26 _______________

Task number 7

Question:

A block of mass 400 g rests on a board. The board is lifted together with the block and released. Find the force (in N) with which the block will act on the board during the flight.

Write down the number:

_______0 ________________

Task number 8

Question:

A person weighing 50 kg swings on a swing, which is attached with two identical ropes. The length of each of the ropes is 2 m. The weight of a person at the moment when he passes the lower point of the trajectory of his movement is 1.2 kN. Find the maximum linear speed (in m/s) at which the person is swinging.

Write down the number:

_______5,29 ___________________

Task number 9

Question:

The car drives over the bridge. At the same time, its weight is reduced. Then this bridge...

Choose one of 4 answer options:

2) Curved down

Curved up

4) Not enough information to draw any conclusions

Task number 10

Question:

The elevator moves up at a speed of 1 m/s. An elevator is loaded with a mass of 100 kg. With what force (in N) does this load act on the elevator during such a movement?

Write down the number: 981

On section DE, the car was moving with uniform acceleration, the acceleration vector is directed opposite to the velocity vector

On section AB, the car moved uniformly

The acceleration module in section AB is less than the acceleration module in section DE.

Solve problems.

9. A body with a mass of 10 kg suspended from a cable rises vertically. With what acceleration does the body move if a cable with a stiffness of 59 kN/m is extended by 2 mm? What is the elastic force in the rope?

Given: SI: Solution:

10. The average height of the satellite above the Earth's surface is 1700 km. Determine the speed of its movement.

Given: SI: Solution:

Solve the problem.

A cart of mass 5 kg moves under the influence of a weight of mass 2 kg. Determine the thread tension if the coefficient of friction is 0.1.

Given: Solution:

OPTION 2

1. The movements of bodies relative to the Earth are listed below. Which frame of reference associated with one of these bodies cannot be considered inertial? The frame of reference associated with the Earth is considered to be inertial.

1) the girl runs at a constant speed

2) the car moves evenly on the horizontal part of the road

3) the train is moving uniformly

4) hockey puck gliding evenly on smooth ice

2. Four forces act on a body with a mass of 2 kg. What is the acceleration of the body if

F 1 \u003d 20 N, F 2 \u003d 18 N, F 3 \u003d 20 N, F 4 \u003d 16 N.

1) 2 m/s 2 2) 4 m/s 2 3) 1 m/s 2 4) 8 m/s 2

3. What expression determines the value of the first space velocity of the satellite, if the radius of its circular orbit is R, and the acceleration of free fall at this height is g?

4. In order for the body in the elevator to experience overload (weight gain), it is necessary:

1) accelerated movement of the elevator up 2) slow movement of the elevator up 3) accelerated movement of the elevator down 4) this state is impossible

5. A man was carrying two identical children on a sled along a horizontal road. Then one child got up from the sled, but the man continued to move at the same constant speed. How did the force of friction change in this case?

1) did not change 2) increased by 2 times 3) decreased by 2 times 4) increased by 50%

6. A block moves evenly up the inclined plane. Which vector shown in the figure is superfluous or incorrect?

7. The speed modulus of a car weighing 1000kg changes in accordance with the graph shown in the figure. Which statement is true?

2) in the CD section, the car was moving with uniform acceleration, the acceleration vector coincides in direction with the velocity vector

3) on the DE section, the car was moving with uniform acceleration, the acceleration vector coincides in direction with the velocity vector

4) the acceleration module in section AB is less than the acceleration module in section DE

7. Using the condition of the problem, match the equations from the left column of the table with their graphs in the right column.

Solve problems.

8. A bus weighing 15 tons starts off with an acceleration of 0.7 m / s 2. What friction force acts on the bus if the engine traction force is 15 kN? Express the answer in kN. What is the coefficient of friction?

Given: SI: Solution:

9. The average height of the satellite above the Earth's surface is 900 km. Determine the speed of its movement.

Given: SI: Solution:

Solve the problem.

10. Two weights of 200 g and 300 g are connected by a thread. Determine the acceleration of the weights and the tension force of the thread between them, if a force of 10 N directed horizontally to the right was applied to a body of mass m 1.

Given: SI: Solution:

Grade _____ teacher's signature ________________ / L.S. Tishkina/

OPTION 3

PART A Choose one correct answer.

1. A skydiver descends vertically at a constant speed of 2 m/s. The frame of reference associated with the Earth is considered to be inertial. In this case:

1) there are no forces acting on the parachute

2) gravity is balanced by the Archimedes force acting on the parachute

3) the sum of all forces acting on the parachute is zero

4) the sum of all forces is constant and not equal to zero

2. Forces of 3 N and 4 N act on a body of mass 2 kg, directed perpendicular to each other. What is the acceleration of the body?

1) 3.5 m/s2 2) 2.5 m/s2 3) 7 m/s2 4) 10 m/s2

3. A satellite of mass m moves around the planet in a circular orbit of radius R. The mass of the planet is M. What expression determines the value of the acceleration of the satellite?

4. A spring scale is installed in the elevator, on which a person stands. How will the readings of the scales change when the elevator moves up and down at an accelerated rate?

1) up - increase, down - decrease

2) up - decrease, down - increase

3) up - increase, down - do not change

4) up - do not change, down - increase

5. A man was carrying a child on a sled along a horizontal road. Then a second similar child sat on the sled, but the man continued to move at the same constant speed. How did the coefficient of friction change in this case?

1) did not change 2) increased by 2 times 3) decreased by 2 times 4) increased by 50%

6. A bar is moving uniformly upward along an inclined plane. Which vector shown in the figure is superfluous or incorrect?

7. The speed modulus of a car weighing 1000 kg changes in accordance with the graph shown in the figure. Which statement is true?

1) on the BC segment, the car was moving uniformly

2) in section CD the car was moving with uniform acceleration, the acceleration vector is directed opposite to the velocity vector.

3) the car was at rest on the EF site

4) the acceleration module in section AB is less than the acceleration module in section DE

8. Using the condition of the problem, match the equations from the left column of the table with their graphs in the right column.

Solve problems.

9. The elevator descends with an acceleration of 2 m/s 2 . In an elevator, a load weighing 0.7 kg hangs on a spring with a stiffness of 560 N/m. What is the spring force? By how many centimeters did the spring lengthen?

Given: Solution:

10. The average height of the satellite above the Earth's surface is 600 km. Determine the speed of its movement.

Given: SI: Solution:

Solve the problem.

11. A bar with a mass of 400 g moves with an acceleration of 0.4 m/s 2 under the action of a load with a mass of 100 g. Find the friction force and the coefficient of friction of the bar against the surface.

Given: SI: Solution:

Grade _____ teacher's signature ________________ / L.S. Tishkina/

OPTION 4

PART A Choose one correct answer

1) the elevator falls freely 2) the elevator rises evenly

3) the elevator is moving slowly up 4) the elevator is moving rapidly down

2. Four forces act on a body of mass 2 kg. What is the acceleration of the body if F 1 = 12 N, F 2 = 18 N, F 3 = 20 N, F 4 = 18 N.

1) 6 m/s 2 2) 16 m/s 2 3) 2 m/s 2 4) 4 m/s 2

3. The mass of the Moon is about 81 times less than the mass of the Earth. What is the ratio of the universal gravitational force F 1 acting from the Earth on the Moon to the force F 2 acting from the Moon on the Earth?

1) 1/81 2) 81 3) 9 4) 1

4. How to make a 10N weight stretch the dynamometer spring with a force greater than 10N?

1) move the dynamometer with the weight down with some acceleration

2) move the dynamometer with the weight up with some acceleration

3) a dynamometer with a weight must fall freely

4) this is impossible to do

5. A man was carrying two identical children on a sled along a horizontal road. Then one child got up from the sled, but the man continued to move at the same constant speed. How has it changed
coefficient of friction?

1) increased by 2 times 2) decreased by 2 times 3) increased by 50% 4) did not change

6. A block lies motionless on an inclined plane. Which vector shown in the figure is superfluous or incorrect?

1) 2) 3) 4)

7. The speed modulus of a car weighing 1000 kg changes in accordance with the graph shown in the figure. Which statement is true?

1) on section CD the car moved uniformly accelerated, the acceleration vector coincides in direction with the velocity vector

2) the acceleration module in section AD is greater than the acceleration module in section DE

3) in section DE the car was moving with uniform acceleration, the acceleration vector is directed opposite to the velocity vector

4) on section AB the car moved uniformly

8. Using the condition of the problem, match the equations from the left column of the table with their graphs in the right column.

Solve problems.

9. A car weighing 1 t moves with an acceleration of 0.8 m / s 2. A friction force of 2 kN acts on the car. Determine the thrust force of the engine (express the answer in kN) and the coefficient of friction.

Given: SI: Solution:

10. The average height of the satellite above the Earth's surface is 300 km. Determine the speed of its movement.

Given: SI: Solution:

Solve the problem.

11. Two loads of masses 200 g and 300 g are suspended on a cord thrown over a fixed block. With what acceleration do the loads move? What is the tension in the thread?

Given: SI: Solution:

Grade _____ teacher's signature ________________ / L.S. Tishkina/

Date "___" _________20____

Task 12 on the topic

"Application of the Law of Conservation of Momentum of a Body"

Solve problems:

1. Find the momentum of a 10 ton truck moving at a speed of 36 km/h and a 1 ton car moving at a speed of 25 m/s.

Given: SI: Solution:

2. A train weighing 2000 tons, moving in a straight line, increased the speed from 36 to 72 km/h. Find the change in momentum.

Given: SI: Solution: Given: SI: Solution:

Given: SI: Solution:

Grade _____ teacher's signature ________________ / L.S. Tishkina/

Date "___" _________20____

Task 15 on the topic

“Formation and propagation of waves.

Examination No. 2

Dynamics.

DEMO VERSION

A1. An airplane flies in a straight line at a constant speed at an altitude of 9 km. The frame of reference associated with the Earth is considered to be inertial. In this case:

1. no forces act on the plane

2. the plane is not affected by gravity

3. the sum of all forces acting on the aircraft is zero

4. gravity is equal to the Archimedes force acting on the plane

A2. Four forces act on a body of mass 2 kg. What is the acceleration of the body if

F 1 \u003d 20 H, F 2 \u003d 18 H, F 3 \u003d 20 H, F 4 \u003d 16 H

A3. A satellite of mass m moves around the planet in a circular orbit of radius R. The mass of the planet is M. What expression determines the value of the satellite's speed?

A4. In order for the body in the elevator to experience overload (weight gain), it is necessary:

accelerated upward movement of the elevator

elevator slow motion up

accelerated downward movement of the elevator

this state is impossible.

A5. A man was carrying a child on a sled along a horizontal road, then a second child of the same type sat on the sled, but the man continued to move at the same constant speed, how did the friction force change in this case?

hasn't changed

increased by 2 times

decreased by 2 times

increased by 50%

A6. A block moves uniformly upward along an inclined plane. Which vector shown in the figure is superfluous or incorrect?

A7. The speed modulus of a car weighing 1000 kg changes in accordance with the graph shown in the figure. Which statement is true?

1. on the BC section, the car moved evenly

2. on the DE section, the car was moving with uniform acceleration, the acceleration vector is directed opposite to the velocity vector

3. on section AB, the car moved evenly

4. the acceleration modulus in section AB is less than the acceleration modulus in section DE

IN 1. Three bodies of the same mass, 2 kg each, made movements. The displacement projection equations are presented in the table. Which graph shows the dependence of the projection of the force on time acting on each body?

IN 2. A body with a mass of 10 kg suspended from a cable rises vertically. With what acceleration does the body move if a cable with a stiffness of 59 kN/m is extended by 2 mm?

IN 3. The average height of the satellite above the earth's surface is 900 km. Determine the speed of its movement. (Give your answer in km/s)