Work, Energy and Power (MCQ Only)

A spring is hung vertically and masses are added to the lower end. The graph shows how the extension Δx of the spring varies with the mass m added.

The work done in extending the spring can be expressed as:

• mg Δx

An object of mass m is moved from point A on the ground, to point B on a bench of height h as shown in the diagram.

Which of the following is a correct expression for the work done on the object?

An object of weight 7 N is raised from a height of 2 m to a height of 8 m. The change in gravitational potential energy is

A cyclist travels up a slope through a vertical height h in a time t. The mass of the cyclist and his bike is m.

The average power of the cyclist is

A motor is used to lift an object as shown. The object is raised through a vertical height of 75 cm at a constant speed of 0.40 m s^-1 with 0.25kg.

Which of the following gives the rate of increase of potential energy of the object in watts?

An object of mass m is moved from the bottom to the top of a slope. The vertical height of the slope is y.

The horizontal distance between the bottom and top of the slope is x.

Which of the following gives the gain of gravitational potential energy of the object as it moves from the bottom to the top of the slope?

• mxy
• mgx
• mgy
• my

A car of mass 1.2 × 10³ kg is travelling at a speed of 18 m s^–1. The driver applies the brakes and the car comes to rest.

What is the work done by the brakes in stopping the car?

• 120 kJ

• 36 kJ

• 250 kJ

• 194.4 kJ