Chapter 4

A man can either take an escalator or a lift to travel up between two floors in a hotel.

The escalator takes 20 seconds to carry the man between the two floors. The useful work done against gravity is W. The useful power developed is P.

The lift takes 30 seconds to carry the same man between the same two floors.

How much useful work against gravity is done by the lift, and how much useful power is developed by the lift?

• more than W and less than P

• more than W and P

• W and less than P

• W and P

Which energy resource is not renewable?

• geothermal

• nuclear fission

• solar

• wind

Two motors X and Y lift loads of the same weight through the same vertical distance.

Motor X is more efficient than motor Y.

Which statement about the motors is correct?

• The useful energy output of motor X is larger than that of motor Y.

• The useful energy output of motor X is smaller than that of motor Y.

• The energy input of motor X is larger than that of motor Y.

• The energy input of motor X is smaller than that of motor Y.

Which energy resource stores kinetic energy?

• coal

• nuclear fission

• solar

• wind

What is the unit of power?

• joule

• newton

• pascal

• watt

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?

• G.P.E: decreases & K.E: decreases

• G.P.E: decreases & K.E: increases

• G.P.E: increases & K.E: decreases

• G.P.E: increases & K.E: increases

Brakes are used to slow down a moving car.

Into which form of energy is most of the kinetic energy converted as the car slows down?

• chemical

• elastic

• thermal

• sound

Which does not transfer useful energy?

• emitting a sound wave

• measuring a temperature

• passing an electric current

• pushing a box along the floor