Y10 C6 Energy Work Power Revision

Which motor produces the most power?

• heavy load, time taken 12 s

• heavy load, time taken 16 s

• light load, time taken 12 s

• light load, time taken 16 s

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

What is the unit of power?

• joule

• newton

• pascal

• watt

A cyclist travels down a hill from rest at point X without pedaling. The cyclist applies his brakes and the cycle stops at point Y. Which energy transfers have taken place between X and Y?

• gravitational potential → kinetic → internal (thermal)

• gravitational potential → internal (thermal) → kinetic

• kinetic → gravitational potential → internal (thermal)

• kinetic → internal (thermal) → gravitational potential

An object of mass m falls from a higher shelf to a lower shelf. How much gravitational potential energy does the object lose?

• mgh₂

• (m/g)h₂

• (m/g)(h₁ - h₂)

• mg(h₁ - h₂)

A box is initially at rest at the top of a rough slope. The box slides down the slope. The weight of the box is 20 N. The slope is 4.0 m long and 2.0 m high. The box does 10 J of work against friction as it slides down the slope. What is the speed of the box as it reaches the bottom of the slope?

• 5.5 m/s

• 6.3 m/s

• 7.1 m/s

• 9.5 m/s