Write true or false for the following statements :

When energy changes from one form to another, the energy that disappears from one form, reappears in exactly equivalents amount in the other form.

A microphone converts:

A. Electrical energy into sound energy in ordinary telephone

B. Microwave energy into sound energy in a mobile phone

C. Sound energy into mechanical energy in a stereo system

D. Sound energy into electrical energy in public address system

A ball falls to the ground as show2n below:

A potential energy = 80 J

Kinetic energy = 0

B Kinetic energy = 48 J

C = potential energy = 0

(a) What is the kinetic energy of ball when it hits the ground?

(b) What is the potential energy of ball at B?

(c) Which law you have made use of in answering this question?

The hanging bob of a simple pendulum is displaced to one extreme position B and then released. It swings towards centre position A and then to the other position C. In which position does the bob have: (i) Maximum potential energy?

(ii) Maximum kinetic energy?

Give reasons for your answer.

Name five appliances or machines which use an electric motor.

A bulb lights up when connected to a battery. State the energy change which takes place:

(i) In the battery.

(ii) In the bulb.

An object is falling freely from a height x. After it has fallen a height, it will possess :

A. Only potential energy

B. Only kinetic energy

C. Half potential and half kinetic energy

D. Less potential and more kinetic energy

Which one of the following statements about power stations is not true?

A. Hydroelectric power stations use water to drive turbines

B. In a power station, turbines drive generators

C. Electricity from thermal power stations differs from that produced in hydroelectric power stations

D. In hydroelectric power stations and thermal power stations, alternators produce electricity.

When an object falls freely towards the earth, then its total energy:

A. Increases B. Decreases

C. Remains constant

D. First increases and then decreases