6 Work, Energy and Power J2019 [End Unit Test]

A machine is very efficient. What does this mean?

• It produces a large amount of power.

• It uses very little energy.

• It wastes very little energy.

• It works very quickly.

An object is lifted vertically by a motor. In which example is the power produced the greatest?

• lifting it a shorter distance in a longer time

• lifting it the same distance in a longer time

• lifting it a shorter distance in the same time

• lifting it the same distance in a shorter time

An object falls under gravity. What happens to the gravitational potential energy and to the kinetic energy of the object?

• decreases, decreases

• decreases, increases

• increases, decreases

• increases, increases

Which motor produces the most power?

• A. heavy load, time taken 12 s

• B. heavy load, time taken 16 s

• C. light load, time taken 12 s

• D. light load, time taken 16 s

A body is lifted against gravity. Which equation shows the work done on the body?

• work done = change in distance moved by the body

• work done = change in energy of the body

• work done = change in force on the body

• work done = change in power of the body

An object falls from the top of a building that is 25 m high. Air resistance is negligible. What is the speed of the object when it hits the ground?

• 10 m/s

• 22 m/s

• 25 m/s

• 625 m/s

A crane takes 2.0 minutes to lift a load to the top of a building. The change in gravitational potential energy of the load is 360 kJ. What is the useful power output of the crane?

• 3.0 kW

• 180 kW

• 720 kW

• 43200 kW

A force F acts on a body and the body moves a distance d in the direction of the force. Which expression for the work done W is correct?

• W = Fd

• W = Fd²

• W = ½ Fd

• W = ½ Fd²

A boy produces an average power output of 60 W as he rides his bicycle for 2.0 minutes. How much useful energy does he expend?

• 0.50 J

• 30 J

• 120 J

• 7200 J

An object is in free fall. The change in gravitational potential energy of the body depends upon its mass m, the change in height Δh and the gravitational field strength g. What is the correct expression for the change in gravitational potential energy?

• gmΔh

• gm/Δh

• gΔh/m

• mΔh/g