UNIT NO.8
Energy
(Solved Exercise)
8.1 Encircle the correct option.
8.2 Write short answer.
1. Name three forms of stored energy?
i. Gravitational potential energy
ii. Elastic potential energy or strain energy
iii. Chemical Energy
2. Dissipated energy is also called wasted energy. Why?
The dissipated forms of energy are wasted without any proper use. Hence, the dissipated enery is also called wasted eneray.
3. Define the law of conservation of energy?
“Energy can neither be created nor be destroyed, but, it can be changed from one form to another.” This fact is known as law of conservation of energy.
4. Where does the energy produced by a dynamo come from?
A dynamo is an electrical device that converts mechanical energy into electrical energy.
8.3 Constructed Response Questions.
1. Fill in the following columns:
- “A” With the form oF energy used by the converter.
- “C” with the form(s) of energy produced by the converter.
| A | B | C |
| Mechanical energy | Dynamo | Eectrical energy |
| Elastic potential energy | Catapult | Kinetic energy |
| Chemical Energy | Burner | Heat Energy |
| Potencial energy | Balloon while blowing up | Kinetic energy |
| Light energy | Tree | Chemical Energy |
2: Which main energy transfer takes place in the following examples?
(a) A child kicking a football.
When a child kicking a football, chemical energy from the child’s muscles is converted into kinetic energy in the child’s leg, which is then transferred to the football, making it move.
(b) A person walking upstairs.
When a person walks upstairs, the primary energy transfer is from chemical energy stored in muscles to gravitational potential energy as they move their body higher against gravity.
(c) Water being boiled in a kettle.
When water is boiled in a kettle, the main energy transfer is electrical energy being converted into thermal energy.
(d) A glowing bulb.
When a glowing bulb is turned on, the main energy transfer is electrical energy being converted into light and heat energy.
3. A driver turns the key of a car engine, the engine sounds ‘rrr rrr rrr’, but does not start. What can be the cause?
A driver turns the key of a car engine, the engine sounds ‘rrr rrr rrr’, but does not start. It shows battery is damaged or the fule is finished.
4. Imagine that you drop down a ball from a certain height. It makes a few bounces from the ground, moves some distance on the ground and finally comes to rest. Your friend says that the ball has lost all of its energy. How will you reponds your friend’s statement in the light of law of conservation of energy?
The ball did not lose all its energy. According to the law of conservation of energy, energy cannot be created or destroyed; it only changes form. While the ball stops bouncing, the kinetic energy from its motion and the potential energy from its height are converted into other forms of energy like sound and heat, which dissipate into the environment.