Work and Energy - Standard 6 - General Science - Balbharati
11. Work and Energy
Exercise
Q. 1 Fill in each blank with the appropriate term.
(a) A bucketful of water is to be drawn from a well. Work will be done when a force is applied to do this, because there will be a displacement of water.
(b) If a ball is dropped on the sloping roof of a house, it acquires motion and falls on the ground. That is, transformation of potential energy into kinetic energy takes place.
(c) Fireworks during Diwali are an example of transformation of chemical energy into light energy.
(d) The solar cooker is an application of the Sun’s heat energy, while solar cells and solar lamps are applications of the Sun’s light energy.
(e) One labourer carried four pans of road metal through 100 metres. If he carries two pans of road metal through a 200 metre distance, equal work will be done.
(f) The capacity that an object has for doing work is called energy.
Q. 2 Match the pairs.
| Group ‘A’ | Group ‘B’ |
|---|---|
| (1) Rolling object | (c) Kinetic energy |
| (2) Food | (e) Chemical energy |
| (3) Stretched bow | (d) Potential energy |
| (4) Sunlight | (a) Heat energy |
| (5) Uranium | (b) Atomic energy |
Q. 3 Can you tell?
(a) When can we say that displacement has taken place?
Ans. When an object’s position changes from its original place due to a force, displacement has taken place.
(b) What should be taken into account for measuring work?
Ans. Both the force applied and the displacement in the direction of that force must be considered.
(c) What are the various forms of energy?
Ans. Mechanical energy (potential and kinetic), heat energy, light energy, sound energy, electrical energy and chemical energy.
(d) Describe one natural chain of transformation of energy.
Ans. Sun’s heat evaporates water (solar → heat). Water stored at height has potential energy; falling water gains kinetic energy (potential → kinetic). Turbines rotate to produce electricity (kinetic → electrical). Electricity can become light (bulb), motion (fan), sound (radio), or heat (heater).
(e) Why should we save energy?
Ans. Conventional resources (coal, petrol, diesel, natural gas) are limited and pollute the environment. Saving energy reduces waste, cuts costs and helps prevent problems like global warming.
(f) What is ‘green energy’?
Ans. Energy from resources that do not produce smoke or carbon gases (like CO2, CO). Examples: solar, wind, small hydel, tidal and wave energy.
(g) What are the non-conventional energy resources?
Ans. Solar energy, wind energy, tidal energy, energy from ocean waves, hydroelectric energy (small hydel), and atomic energy.
(h) Which forms of energy from the sun are used in solar energy devices?
Ans. Heat energy (solar cooker, water heater, dryer) and light energy (solar cells/solar panels).
(i) Why should we maximise the use of non-conventional energy resources?
Ans. They are renewable/inexhaustible and cleaner, reduce dependence on exhaustible fossil fuels, and help protect the environment.
Q. 4 Who is the odd-one-out? (Give reason)
(1) Diesel, crude oil, natural gas.
Ans. Wind. Reason: Wind is renewable; others are non-renewable.
(2) A running car, hauling a log, a book kept on a table, picking up the school bag — Odd: Book on a table (no displacement/work).
(3) Sunlight, wind, waves, petrol — Odd: Petrol (non-renewable fuel); others are renewable sources.
(4) Leaving the fan on in a vacant room, leaving the TV on while working, using AC during winter, putting off the light when going out — Odd: Putting off the light (saves energy); others waste energy.
5. Find out the types of energy from the following puzzle.
| z | s | q | p | y | m | w | n | e |
| p | o | t | e | n | t | i | a | l |
| l | l | s | u | h | v | n | x | i |
| t | a | o | j | e | v | d | z | g |
| q | r | u | l | a | b | a | d | h |
| k | i | n | e | t | i | c | q | t |
| r | w | d | h | k | l | w | y | f |
