Energy, work and power — final check

1. state / describe

(a) State the energy store of each of these: a hammer raised above a nail; the plutonium in the power pack of a space probe; hot water in a bath. (b) State four ways in which energy can be transferred from one store to another. (c) State the principle of the conservation of energy. (d) An electric fan, plugged into the mains, is switched on. Describe the energy transfers from the mains to the moving blades and the surroundings.

(a) Three stores

(b) Four ways of transfer

(c) Conservation of energy

(d) The fan

2. calculate

Each second, 500 J of light from the Sun falls on a solar panel. 400 J of it heats the panel and the air, and the rest leaves the panel by electrical work. The current carries this energy to a lamp, but 10 J heats the wires on the way. The lamp gives out 18 J of light, and the rest heats the lamp and the air. (a) Calculate the energy that leaves the panel by electrical work each second. (b) Calculate the energy that heats the lamp and the air each second.

(a) Energy leaving the panel by electrical work: ______________ unit ________

(b) Energy heating the lamp and the air: ______________ unit ________

3. calculate / define

A forklift truck lifts a crate of weight 6000 N through a height of 2.0 m in 4.0 s. (a) Calculate the work done on the crate. (b) In those 4.0 s, the forklift’s motor takes 20 000 J from its battery. Calculate the power supplied to the motor by the battery. (c) Define power.

(a) Work done: ______________ unit ________

(b) Power supplied by the battery: ______________ unit ________

(c) The definition of power

4. calculate

A 0.20 kg ball is thrown straight upwards at 8.0 m/s. Air resistance is small enough to ignore. (a) Calculate its kinetic energy as it leaves the hand. (b) Calculate the greatest height it rises above the hand. Give your answer to 2 significant figures.

(a) Kinetic energy: ______________ unit ________

(b) Greatest height, to 2 significant figures: ______________ unit ________