Y12 Work, Energy and Power

Two trolleys are held together on a horizontal surface with a compressed spring between them. When they are released, the trolleys lose contact with the spring. The trolley of mass 2 kg moves to the left at a final speed of 2 m s^-1. How much elastic potential energy was stored in the spring?

• 4 J

• 6 J

• 8 J

• 12 J

A spring is compressed by a mass, as shown. Which statement describes the changes to the energy of the spring when it is compressed by the mass?

• The spring gains both gravitational potential energy and elastic potential energy.

• The spring gains gravitational potential energy and loses elastic potential energy.

• The spring loses both gravitational potential energy and elastic potential energy.

• The spring loses gravitational potential energy and gains elastic potential energy.

A man of mass 75 kg runs up a staircase consisting of 30 steps. Each step is 20 cm high.

The man takes a time of 7.0 s to run from the bottom of the staircase to the top.

What is the average rate of increase of gravitational potential energy of the man?

• 64 W

• 450 W

• 630 W

• 4400 W

A lamp is switched on for 2.0 hours. The power input to the lamp is 1.0 W. The energy given out

by the lamp as light is 7.0 x 10³J.

How much energy is converted to other forms by the lamp?

• 120 J

• 200 J

• 3400 J

• 7200 J

A man sits on a buggy that is pulled along by a wire attached to a kite. The wire is at an angle of 40⁰ to the horizontal and has a constant tension of 200 N. The man and buggy travel a distance of 20 m along a straight horizontal path. The wire and the path of the buggy are in the same vertical plane. What is the work done by the tension force on the man and buggy?

• 2.6 kJ

• 3.1 kJ

• 3.4 kJ

• 4.0 kJ

A ball is thrown vertically upwards from the surface of the Earth. Which statement describes the energy of the ball as it rises through the air?

• The kinetic energy of the ball decreases as the gravitational potential energy decreases.

• The kinetic energy of the ball decreases as the gravitational potential energy increases.

• The kinetic energy of the ball increases as the gravitational potential energy decreases.

• The total energy of the ball increases.

The force–extension graph for a spring is shown. What represents the work done to extend the spring?

• the area under the graph

• the gradient of the graph

• the reciprocal of the gradient of the graph

• twice the area under the graph

A steam turbine is used to drive a generator. The input power to the turbine is P_I and the output

power is P_o. The power loss in the turbine is P_L, as shown. What is the efficiency of the turbine?

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