This test contains 23 options for assignments of different levels on the topic "Work, power, simple mechanisms" for the 9th grade (according to the physics textbook for the 9th grade by the authors Shakhmaev N.M., Bunchuk A.V.). Each option contains a different number of quality and design problems of different levels. Knowing individual characteristics student, in this work, you can select tasks that are feasible for each child. I would be glad if this publication is useful to someone. Download, recycle. Good luck!

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9kl. (according to Shakhmaev).

Examination work No. 3.

Work, power, simple mechanisms.

Option number 1

1. A body weighing 1 kg with a force of 20 N rises to a height of 5 m. What is the work of this force?
2. Give a detailed answer: is it possible to move a sailboat by directing a stream of air from a powerful fan on the boat to the sails?
3. Determine the minimum power that the lift motor must have to lift a 50kg load to a height of 10m in 5s. Find efficiency
4. What work is done by the force of gravity acting on a raindrop weighing 20 g when it falls from a height of 1 km?

Option number 2

1. A body weighing 1kg rises to a height of 5m. What is the work of gravity?
2. Give a detailed answer: a stone and a tennis ball are hit with a stick. Why does the ball fly farther than a stone, other things being equal?
3. Calculate the power of the pump that delivers 1200kg of water every minute to a height of 20m.
4. A stone weighing 400 g was thrown vertically upward at a speed of 20 m / s. What are the kinetic and potential energy of a stone at a height of 15m?
5. A piano weighing 300 kg was fed into the sixth floor window, located 16 m above the sidewalk, using a lifting device in 50 seconds. Determine the work, power, efficiency.

Option number 3

1. The weightlifter, lifting the barbell, performs a work of 5 kJ in 2 s. Determine the power and efficiency.
2. What weight can the lifting machine lift to a height of 30 m in 4 minutes if the engine power is 5 kW?

Option number 4

1. Kot Matroskin and Sharik towed Uncle Fyodor's car to Prostokvashino for 1 hour, acting with a force of 120 N. Distance to Prostokvashino is 1 km. Determine the work, efficiency and power
2. What is the power developed by a tractor at a speed of 9.65 km / h and a pulling force of 15 kN?
3. What work is done with a uniform lifting of an iron beam with a volume of 0.1 m 3 to a height of 15 m?

Option number 5

1. 1.A boy weighing 40 kg climbed in 30 seconds to the second floor of the house, located at a height of 8 m. Determine the work and power
2. What kind of work does an excavator do when lifting 14 m of soil with a bucket? 3 to a height of 5 m? Soil density 1400 kg / m 3 .
3. The climber climbed in the mountains to a height of 2 km. Determine the mechanical work performed by the climber during the ascent if his weight with equipment is 85 kg.
4. How much weight can the lifting machine lift to a height of 30 m in 4 minutes, if the engine power is 5 kW? Find efficiency
5. A force of 4 N and 20 N acts at the ends of the lever, the length of the lever is 1.5 m. Where is the fulcrum if the lever is in equilibrium?

Option number 6.

1. A person, walking for 2 hours, makes 10,000 steps (in one step, work is done 40 J). Determine the work, power and efficiency.
2. What work is done by the force of gravity acting on a raindrop weighing 20 g when it falls from a height of 2 km?
3. The thrust force of a supersonic aircraft at a flight speed of 2340 km / h is 220 kN. Find the power of the aircraft engines in this flight mode.
4. Weights of 4 and 24 kg are suspended from the lever. The distance from the fulcrum to the larger load is 4 cm. Determine the length of the arm if the arm is in equilibrium.

Option number 7

1. The Baba Yaga stupa (weight 70 kg) flies 120 km in 1 hour. Determine the work, power
2. The crane lifted a load weighing 5 tons to a height of 10 m in 45 seconds. Determine the crane motor power and efficiency
3. The diesel locomotive develops a traction force of 400 kN at a speed of 54 km / h. What work is done to move the train within 1 minute?
4. A force of 4 N and 20 N acts at the ends of the lever, the length of the lever is 1.5 m. Where is the fulcrum if the lever is in equilibrium?

Option number 8

1. Carlson lifts the Kid weighing 30 kg to the roof of a house 20 m high in 10 seconds. Determine the work and power of Carlson
2. The spring of a toy pistol, compressed by 3 cm, pushes the ball out in 1 s, acting on it with a force of 10N. Determine the work, power and efficiency.
3. The Zhiguli car travels 100 m in 6.25 s, developing a thrust of 3 kN. Determine work and power
4. 4. The atomic icebreaker, developing a power of 32400 kW, covered 20 km in 5 hours. Determine the average force of resistance to the movement of the icebreaker.
5. Weights of 4 and 24 kg are suspended from the lever. The distance from the fulcrum to the larger load is 4 cm. Determine the length of the arm if the arm is in equilibrium.

Option number 9.

1. The crane lifts a concrete slab weighing 5 tons to a height of 9 m for 1 minute. Determine the work, power and efficiency.
2. The boy evenly lifted the bucket of water from the well once in 20 seconds, and the other in 30 seconds. Was the same work done in these cases? What can you say about the power when performing these works?
3. The cyclist performed 800 J in 10 seconds. What is the power of the cyclist?
4. How much weight can the lifting machine lift to a height of 30 m in 4 minutes, if the engine power is 5 kW?
5. A force of 4 N and 20 N acts at the ends of the lever, the length of the lever is 1.5 m. Where is the fulcrum if the lever is in equilibrium?

Option number 10

1. How long will it take to pump out water weighing 2 tons, if the pump power is 1.5 kW? The height of the water rise is 20 m. Find the efficiency.
2. Academician B.S. Jacobi invented the electric motor in 1834. In the first version, the electric motor lifted a 5 kg load to a height of 60 cm in 2 s. Determine the engine power.
3. What is the power developed by a tractor at a speed of 9 km / h and a pulling force of 10 kN?
4. The atomic icebreaker, developing a power of 32400 kW, covered 20 km in 5 hours. Determine the average force of resistance to the movement of the icebreaker.
5. Weights of 4 and 24 kg are suspended from the lever. The distance from the fulcrum to the larger load is 4 cm. Determine the length of the arm if the arm is in equilibrium.

Option number 11

1. .How to what height do you need to lift a weight of 100 N in order to do the work?

200 J?

1. Determine the work done when lifting a 4 N load to a height of 4 m
2. Determine the work done by a 400 W motor in 30 seconds. What is the efficiency?
3. How much weight can the lifting machine lift to a height of 30 m in 4 minutes, if the engine power is 5 kW?
4. A force of 4 N and 20 N acts at the ends of the lever, the length of the lever is 1.5 m. Where is the fulcrum if the lever is in equilibrium?

Option number 12

1. How long does a 200 W electric motor have to run to do 2500 J?
2. When cycling on a horizontal road at a speed of 9 km / h, a power of 30 watts is generated. Find the driving force.
3. Calculate the power of the pump, which delivers 1200 kg of water every minute to a height of 20m

1. The nuclear icebreaker, developing a power of 32,400 kW, covered 20 km in ice in 5 hours.
2. Determine the average force of resistance to the movement of the icebreaker and efficiency. icebreaker
3. Weights of 4 and 24 kg are suspended from the lever. The distance from the fulcrum to the larger load is 4 cm. Determine the length of the lever if the lever is in

balance.

Option number 13

1. The crane lifts the load at a constant speed of 5.0 m / s. Crane power 1.5 kW. Which

can the load be lifted by this crane?

1. When preparing a toy pistol for a shot, a spring with a stiffness of 800 N / m

squeezed by 5 cm. What velocity will a 20 g bullet acquire when fired horizontally?

1. A force of 4 N and 20 N acts at the ends of the lever, the length of the lever is 1.5 m. Where is the fulcrum if the lever is in equilibrium?

Option number 14

1. A ball weighing 100 g freely fell onto a horizontal platform, having a velocity of 10 m / s at the moment of impact. Find the height of the fall, neglect friction.
2. 1.8 ∙ 10 falls from a dam with a height of 20 m 4 tons of water. What kind of work is being done?
3. Determine the potential energy of a spring with a stiffness of 1.0 kN / m if it is known that the compression of the spring is 30 mm.
4. Carlson lifts the Kid weighing 20 kg to the roof of a house 20 m high in 10 seconds. Determine the work and power of Carlson

Option number 15

1. Determine the net engine power of a motorcycle if its pulling force is 350 N at 108 km / h.
2. What work is done when lifting from the ground the materials necessary to build a column 20 m high with a cross-sectional area of ​​1.2 m 2 ? The density of the material is 2.6 ∙ 10 3 kg / m 3.
3. Determine how fast you need to throw the ball down from a height of 3 m so that it bounces to a height of 8 m.
4. A force of 4 N and 20 N acts at the ends of the lever, the length of the lever is 2 m. Where is the fulcrum if the lever is in equilibrium?

Option number 16

1. With an aircraft speed of 900 km / h, its four engines develop a net power of 30 MW. Find the thrust of each engine in this flight mode.
2. Determine the work to be done when digging a well with a diameter of 1.0 m and a depth of 10 m, if the density of the soil is 1.8 ∙ 10 3 kg / m 3 ... Consider that the soil is scattered in a thin layer over the surface of the earth.

3. A stone weighing 20 g, released vertically upward from a slingshot, a rubber band that was stretched by 10 cm, rose to a height of 40 cm. Find the stiffness of the spring.

4. Determine the minimum power that the hoist motor must have to lift a 50kg load to a height of 10m in 5s. Find efficiency

Option number 17

1. The crane evenly lifts a load weighing 500kg to a height of 10m in 50s. Determine the efficiency of the crane if its motor power is 1.5 kW.
2. The spring, compressed to 30cm, is fully extended. What work did the elastic force do if the spring rate is 100N / m?
3. Determine the work of the friction force if a body with a mass of 2 kg changes its speed from 4 to 3 m / s?
4. A 250g ball is thrown vertically upward at a speed of 20m / s. What is its kinetic energy at a height of 10m.

Option number 18

1. The box is pulled evenly along a horizontal surface by a rope forming an angle of 60 ° with the horizon. The force applied to the rope is 25N. What kind of work is done when the box is moved at a distance of 4m?
2. At an altitude of 15m above the Earth's surface, the building block has a potential energy of 1500 kJ. What is its mass equal to?
3. The spring has a stiffness of 2500 N / m. What energy does the spring have when compressed by 10cm?
4. An arrow weighing 20 g is fired from the bow vertically upward at a speed of 20 m / s. Determine its kinetic energy at a height of 15m.
5. The atomic icebreaker, developing a power of 32400 kW, covered 20 km in ice in 5 hours. Determine the average force of resistance to the movement of the icebreaker and efficiency. icebreaker

Option number 19

1. A body weighing 1kg with a force of 20N rises to a height of 5m. What is the work of this force?
2. The ball, lowered under water to a depth of 30 cm, is pushed out with a force of 5N. Define the job.
3. The spring is compressed by 4 cm. The spring rate is 100 kN / m. What kind of work will she do?
4. Useful work 20kn, all consumed energy is equal to 40,000 N. Find efficiency
5. Name the transitions of energy when falling

Option number 20

1. Weights of 4 and 24 kg are suspended from the lever. The distance from the fulcrum to the larger weight is 4 cm. Determine the distance to the second weight if the arm is in balance.
2. The spring is compressed by 50 cm. The spring rate is 10 kN / m. What is the energy of the spring?
3. Determine the work of gravity when a body weighing 4 kg falls from a height of 200 cm.
4. What is meant by the energy of the body? List the types of energy.

Option number 21

1. The climber climbed in the mountains to a height of 1.5 km. Determine the mechanical work performed by the climber during the ascent if his weight with equipment is 100 kg.
2. What is the payoff for the movable block?
3. Write down formulas different types energies
4. Where and for what purpose is the gate used?

Option number 22

2. What is the inclined plane used for?

3. The spring, compressed by 10cm, is fully extended. What work has been done by the elastic force if the spring rate is 1kN / m?

4. At a height of 10m above the Earth's surface, the building block has a potential energy of 150 kJ. What is its mass equal to?

Option number 23

1. What is the payoff for the movable block?

2. A nuclear icebreaker, developing a power of 32400 kW, covered 20 km in ice in 5 hours. Determine the average force of resistance to the movement of the icebreaker.

3. Weights of 4 and 24 kg are suspended from the lever. The distance from the fulcrum to the larger load is 4 cm. Determine the length of the arm if the arm is in equilibrium.

4. Carlson lifts the Kid weighing 30 kg to the roof of a house 20 m high in 10 seconds. Determine the work and power of Carlson

Option number 24

1. The crane lifts the load at a constant speed of 5.0 m / s. Crane power 1.5 kW. What kind of load can this crane lift?
2. Determine at what height the kinetic energy of a ball thrown vertically upward at a speed of 23 m / s is equal to its potential?
3. When preparing a toy pistol for a shot, the spring with a stiffness of 800 N / m was compressed by 5 cm. What velocity will a 20 g bullet acquire when fired horizontally?
4. Forces of 5 and 6 N act on the lever from below at angles of 45 and 30 degrees at a distance of 20 and 40 cm, respectively, from the support located in the middle of the lever. Find the force that can balance the system by applying it vertically at a distance of 10 cm from the axis of rotation.

Conversion of mechanical energy... Mechanical energy is not conserved during any interactions of bodies. The law of conservation of mechanical energy is not fulfilled if friction forces act between the bodies.

Experience shows that mechanical movement never disappears without a trace and never arises by itself. During the braking of the vehicle, heating of the brake pads, vehicle tires and asphalt occurred. Consequently, as a result of the action of friction forces, the kinetic energy of the car did not disappear, but turned into the internal energy of the thermal motion of molecules.

For any physical interactions energy does not arise and does not disappear, but only transforms from one form to another.

This experimentally established fact is called the law of conservation and transformation of energy.

The main task of mechanics - determining the position of a body at any moment in time - can be solved using Newton's laws, if the initial conditions and forces acting on the body are given as functions of coordinates and velocities (and time). In practice, these dependencies are not always known. However, many problems in mechanics can be solved without knowing the values ​​of the forces acting on the body. This is possible because there are quantities that characterize the mechanical movement of bodies, which are preserved under certain conditions. If the position of the body and its speed at a certain moment of time are known, then using the conserved quantities it is possible to determine the position and speed of this body after any interaction, without resorting to the laws of dynamics.

The quantities conserved in mechanical processes are momentum, angular momentum and energy.

Body impulse. We multiply the expression for Newton's second law in the form F = ma (under the action of a constant force F) by Δ t: F * Δt = ma * Δt = m Δ v = m (v 2 - v 1) = mv 2 - mv 1 = Δ (mv). The quantity p = mv is called the momentum of the body(otherwise - by the amount of motion), F Δ t - by the impulse of force. Using these concepts, Newton's second law can be formulated as follows: the momentum of the forces applied to the body is equal to the change in the momentum of the body; F Δ t = Δ p (18)

Momentum conservation law... When considering a system of bodies, one should take into account that each of them can interact both with bodies belonging to the system and with bodies that are not part of this system. Let there be a system of two material points interacting with each other. Let us write Newton's second law for each of the material points of the system under consideration for the time interval Δ t:

(F 1 + F 21) Δ t = Δ p 1

(F 2 + F 12) Δ t = Δ p 2

Adding both equalities, we get: Δ p 1 + Δ p 2 = (F 1 + F 21) Δ t + (F 2 + F 12) Δ t

According to Newton's third law, F 12 + F 21 = 0, therefore, the change in the momentum of the entire system, equal to the vector sum of the changes in the momenta of its constituent particles, looks like this:

In inertial reference frames, the change in the total momentum of a system of material points is equal to the momentum of all external forces acting on this system.

A system of bodies that are not acted upon by external forces or the sum of all external forces is zero is called closed. Impulse conservation law: in a closed system of bodies, the momentum of the system is conserved. This conclusion is a consequence of Newton's second and third laws. The law of conservation of momentum is not applicable to open systems of bodies; however, the projections of the momentum on the coordinate axes remain constant, in the direction of which the sum of the projections of the applied external forces is equal to zero.

Jet propulsion... Consider, as an example, the operation of a jet engine. When fuel is burned, gases heated to a high temperature are ejected from the rocket nozzle. These gases are ejected from the nozzle at a speed. This speed is called the flow rate. Neglecting the interaction of the rocket with external bodies, we will consider the system of bodies "rocket - gases" closed. Let at the moment of time t 0 = 0 a rocket of mass m was moving at a speed of v 0. For a small time interval Δ t, a mass of gas Δ m is ejected from the rocket with the speed and relative to the rocket, that is, with the speed V 1 = u + v relative to the inertial reference frames (here v is the rocket speed). According to the law of conservation of momentum, we have: MV 0 = (m - Δ m) v + Δ mV 1 Substituting the values ​​V 1 = u + v, v = V 0 + Δ v, we get: M Δ v = - Δ μ

Let us divide both sides of the equality by the time interval Δ t, during which the rocket engines worked: m (Δv / Δ t) = - (Δ m / Δ t) u. The product of the rocket mass m and the acceleration of its motion a is called the reactive thrust force: F p = ma = - μu (19). The reactive thrust force acts from the side of the outflowing gases on the rocket and is directed in the direction opposite to the direction of the outflow of gases.

Test questions and tasks:

1. Formulate a definition of work force. In what units is work measured? What is the physical meaning of the job?

2. Under what conditions is the work of force positive? negative? is zero?

3. What is the definition of potential energy? Where is the minimum potential energy?

4. Formulate the definition of the kinetic energy of the body and the kinetic energy theorem.

5. Give the definition of power. What are the scalar or vector quantities of power?

6. On what quantities does the work of the elastic force depend?

7. What is called the total mechanical energy of the system? Formulate the law of conservation of mechanical energy, and under what conditions is it fulfilled?

8. Give the definition of body impulse. Formulate the law of conservation of momentum.

9. What is the jet motion of the body?

10. The tower crane lifts in a horizontal position a steel beam 5 m long and 100 cm 2 section to a height of 12 m. What useful work does the crane do?

11. What kind of work does a person perform when lifting a load weighing 2 kg to a height of 1 m with an acceleration of 3 m / s 2?

12. The speed of a freely falling body weighing 4 kg on a certain path increased from 2 to 8 m / s. find a job of gravity along the way.

13. A wooden container weighing 200 kg was evenly moved along the wooden floor at a distance of 5 m. Find the work done during this movement. Sliding friction coefficient 0.5.

14. When the spring is stretched by 2 cm, a work of 1 J is done. What work should be done to stretch the spring by another 2 cm?

15. What is the minimum power of the hoist motor to lift a 100 kg load to a height of 20 m in 9.8 seconds.

16. Find the maximum height to which a stone thrown vertically upward at a speed of 20 m / s will rise.

17. The movement of a material point is described by the equation x = 5 - 8t + 4t 2. Taking its mass equal to 2 kg, find the impulse in 2 s and 4 s after the start of the time count, as well as the force that caused this change in impulse.

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

19. A car with a mass of 2 tons braked and stopped, having covered a distance of 50 m. Find the work of the friction force and the change in the kinetic energy of the car if the road is horizontal and the coefficient of friction is 0.4.

20. At what speed did a train with a mass of 1500 tons move if, under the action of a braking force of 150 kN, it traveled a distance of 500 m from the moment of braking to a stop?

1. In rectilinear motion, the speed of a material point is directed: 1) to the same direction as the movement; 2) against the direction of movement; 4) regardless of the direction of movement;
2. A physical quantity equal to the ratio of the movement of a material point to a physically small period of time during which this movement occurred is called 1) the average speed of the uneven movement of a material point; 2) the instantaneous speed of a material point; 3) the speed of uniform movement of a material point.
3. In which case is the acceleration modulus greater? 1) the body moves at a high constant speed; 2) the body is rapidly gaining or losing speed; 3) the body is slowly gaining or losing speed.
4. Newton's third law describes: 1) the action of one body on another; 2) the action of one material point on another; 3) the interaction of two material points.
5. The locomotive is coupled to the carriage. The force with which the locomotive acts on the car is equal to the forces that impede the movement of the car. Other forces do not affect the movement of the carriage. Consider the frame of reference connected to the Earth as inertial. In this case: 1) the carriage can only be at rest; 2) the car can only move at a constant speed; 3) the carriage is moving at a constant speed or is at rest; 4) the car is moving with acceleration.
6. An apple weighing 0.3 kg falls from the tree. Choose the correct statement 1) the apple acts on the Earth with a force of 3H, and the Earth does not act on the apple; 2) The Earth acts on the apple with a force of 3H, and the apple does not act on the Earth; 3) the apple and the Earth do not act on each other; 4) the apple and the Earth act on each other with a force of 3 N.
7. Under the action of a force of 8N, the body moves with an acceleration of 4m / s2. What is its mass equal to? 1) 32 kg; 2) 0.5kg; 3) 2 kg; 4) 20kg.
8. With dry friction, the maximum force of static friction is: 1) greater than the force of sliding friction; 2) less sliding friction force; 3) is equal to the sliding friction force.
9. The force of elasticity is directed: 1) against the displacement of particles during deformation; 2) in the direction of particle displacement during deformation; 3) nothing can be said about its direction.
10. How do the mass and weight of a body change when it moves from the equator to the pole of the Earth? 1) the mass and weight of the body do not change; 2) body weight does not change, weight increases; 3) body weight does not change, weight decreases; 4) body weight and weight decrease.
11. The spacecraft after turning off the rocket engines moves vertically upward, reaches the top point of the trajectory and then moves downward. On what part of the trajectory in the ship is the state of weightlessness observed? Air resistance is negligible 1) only during upward movement; 2) only during downward movement; 3) only at the moment of reaching the top point of the trajectory; 4) during the entire flight with inoperative engines.
12. An astronaut on Earth is attracted to it with a force of 700N. With what approximately force will it be attracted to Mars, being on its surface, if the radius of Mars is 2 times, and the mass is 10 times less than that of the Earth? 1) 70N; 2) 140 N; 3) 210 N; 4) 280H.
Part 2
1) The body is thrown at an angle to the horizon with an initial speed of 10 m / s. What is the speed of the body at the moment when it was at a height of 3 m? Determine the force of gravity acting on a body with a mass of 12 kg, lifted above the Earth at a distance equal to a third of the Earth's radius.
2) What work needs to be done to lift a 30 kg load to a height of 10 m with an acceleration of 0.5 m / s2?