RBSE Solutions for Class 8 Science Chapter 9 Work and Energy
RBSE Solutions for Class 8 Science Chapter 9 Work and Energy
Rajasthan Board Solutions for Class 8 Science Chapter 9 Work and Energy
Work and Energy Textbook Questions Solved
I. Multiple Choice Questions
Question 1.
- The unit of energy is:
(a) Newton
(b) Kilogram
(c) Joule
(d) Watt - The capacity of doing work is called:
(a) power
(b) force
(c) momentum
(d) energy - One of the following is not fossil fuel:
(a) petrol
(b) wood
(c) natural gas
(d) diesel - Which of the following apparatus used to convert electric energy into sound energy:
(a) electric motors
(b) electric magnet
(c) electric heater
(d) electric bell
Answers:
- (c)
- (d)
- (b)
- (d)
Question 2.
Pill in the blanks.
- The energy in objects due to its motion is called…………………of an object.
- Stressing the rubber in sling-shot, the…………………energy is stored in it.
- Electric cell used in household, converts…………………energy into electric energy.
- Unit of energy is…………………
Answers;
- Kinetic energy
- Potential
- Chemical
- Joule
Question 3.
Match the column A with column B.
| (A) Energy conversation | (B) Instruments |
| (i) Electrical energy to sound energy | (a) Solar cell |
| (ii) Electrical energy to heat energy | (b) Dynamo (generators) |
| (iii) Mechanical energy to electrical energy | (c) Electric heater |
| (iv) Light energy to electrical energy | (d) Speaker |
Answer:
| (A) Energy conversation | (B) Instruments |
| (i) Electrical energy to sound energy | (a) Speaker |
| (ii) Electrical energy to heat energy | (b) Electric heater |
| (iii) Mechanical energy to electrical energy | (c) Dynamo (generators) |
| (iv) Light energy to electrical energy | (d) Solar cell |
Work and Energy Short Answer Type Questions
Question 1.
Define work.
Answer:
The action for producing the displacement by exerting force on object is called work.
Question 2.
What are the things on which work done on the object depend?
Answer:
(i) Distance covered by an object.
(ii) Amount of force applied on it, thus, Work = Force x Displacement.
Question 3.
Give the two names which store kinetic energy and potential energy in it on the basis of daily life observation.
Answer:
Water in the overhead tanks and striking hammer have potential as well as kinetic energies. Flying bird and running fan have both potential as well as kinetic energies.
Question 4.
How do we define heat energy conversation? Explain energy transfer on the basis of three different examples.
Answer:
Energy stored in burinng objects of hot objects. When this energy is converted from one form into another form, it is called heat energy conversation.
Examples:
(a) Electric heater converts electric energy to heat energy.
(b) Solar cell converts light energy to electric energy.
(c) Electric generator converts mechanical energy to electric energy.
Work and Energy Long Answer Type Questions
Question 1.
What do you mean by global energy crisis? What are the measures adopt to resolve the global energy cirisis? Describe it in detail.
Answer:
Due to growing population and development in different fields, demand and use of traditional energy sources is continuously increasing. The storage of deposits of these resources is limited, a day will come when these deposits would exhaust if their use is done with the same speed and manner. It would result into energy crisis. Hence it is essential that we should use them wisely and try to find alternate sources of energy and increase their use.
Measures of conservation energy:
- Use electric appliances when needed
- When no body is in the room electric appliances should be switched off.
- Use solar cooker, pressure cooker etc to save energy.
- Avoid wastage of traditional sources of energy.
- Close the engines of automobiles while waiting of any one or at traffic points.
- Optimum use of solar energy.
- Use of biotic energy resources.
- Such techniques should be used in building construction so they may remain cool in summers and warm in winter so less use for A.C, heater and electricity could be saved’
- LED bulbs and tube lights should be used in place of ordinary bulbs and tube light to save energy.
- Regular checkup and servicing of vehicles.
Question 2.
Explain the differences between conventional energy sources and non-conventional energy sources with providing suitable example.
Answer:
The differences between conventional energy sources and non-conventional energy sources are as follows:
| Conventional sources of energy | Non-conventional sources of energy |
| (i) Their decomposition rate is less than the consumption rate. | (i) Their decomposition rate is higher than the consumption rate. |
| (ii) These sources of energy can be used limited and in controlled quantity as their reserves are limited. | (ii) These sources of energy can be used continuously because their reserves are unlimited. |
| (iii) Traditional sources of energy create pollution. | (iii) Non-traditional sources of energy are environment friendly hence do not create pollution. |
| (iv) These are limited energy sources. | (iv) These are unlimited energy sources. |
| (v) Petrol, diesel, coal, natural gas, etc. fossil fuels and wood are traditional sources of energy used by us. | (v) Sun, sea, water, air’ and earth, etc. are non-traditional sources of energy. |
Work and Energy Additional Questions Solved
I. Multiple Choice Questions
Question 1 .
When the displacement produced in a body is perpendicular to the direction of applied force then work done is:
(a) 1 Joule
(b) Zero Joule
(c) 103 Joule
(d) None of these
Question 2.
Energy possesse by virtue of its position is called-
(a) Mechanical energy
(b) Chemical energy
(c) Kinetic energy
(d) Potential energy
Question 3.
Which of the following is not a fossil fuel?
(a) Fire wood
(b) Natural gas
(c) Wind energy
(d) Kerosene
Question 4.
Which of the following converts chemical energy into electrical energy?
(a) Solar cell
(b) Bulb
(c) Battery
(d) Dynamo
Question 5.
When the velocity of a body is doubled, then its kinetic energy will become
(a) 8 times
(b) 4 times
(c) 16 times
(d) None of these
Question 6.
What type of energy is used to run submarine?
(a) Wind energy
(b) Ocean energy
(c) Atomic”energy
(d) None of these
Question 7.
Energy obtained from the Sun, wind, water, bio waste, oceans, underground energy is known as
(a) Non- conventional energy
(b) Conventional energy
(c) Ocean energy
(d) None of these
Question 8.
The energy of tides and currents in ocean can be converted into electrical energy, such energy is known as:
(a) Mechanical energy
(b) Ocean energy
(c) Atomic energy
(d) None of these
Question 9.
The unit of energy is
(a) Watt
(b) Kilometre/hour
(c) Joule/sec
(d) Watt/sec
Question 10 .
The combination of kinetic energy and potential energy is
(a) Electrical energy
(b) Mechanical energy
(c) Geo-thermal energy
(d) Bio energy
Question 11 .
Which form of energy is contained in wind energy?
(a) Kinetic energy
(b) Potential energy
(c) Electric energy
(d) Thermal energy
Answers:
1. (b)
2. (d)
3. (c)
4. (c)
5. (b)
6. (c)
7. (a)
8.(b)
9. (a)
10. (b)
11. (c)
Work and Energy Very Short Answer Type Questions
Question 1.
Define the term energy. Give its S.I unit.
Answer:
The capacity of doing work is called energy. Its S.I unit is Joule.
Question 2.
Name the place, where the atomic power plant is located in Rajasthan.
Answer:
Rawatbhata in Chittorgarh, Rajasthan.
Question 3.
What is the full form of LPG?
Answer:
The full form of LPG is Liquified Petroleum Gas.
Question 4.
Define Geo-thermal energy?
Answer:
Energy persent in the depth of the earth is called Geothermal energy. As we move inside the earth from the earth surface the temperature increases with increasing depth. This heat energy can be converted into electrical energy.
Question 5.
Define wind mill. Give its two uses.
Answer:
Wind mill is a machine which convert wind energy into mechanical energy. Wind mills are used for grinding of wheat and lifting water from the well.
Question 6.
What are renewable energy sources?
Answer:
Non conventional energy sources are called renewable energy sources. These are the sources which can be re-constituted or redeveloped. Important non conventional energy sources are solar energy, wind energy, bio mass, bio gas etc.
Question 7.
What is the other name of conventional energy sources?
Answer:
Conventional energy sources are also known as non renewable energy sources. Those energy sources which cannot be re-plenished such as coal, petrol, water, nuclear power etc. are non-renewable sources.
Question 8.
Define fossil fuel.
Answer:
Millions of years back when plants vegetation and animals present at that movement were supressed in the earth due to the excessive pressure and temperature is known as fossil fuel. Example are coal, petroleum, gas etc.
Question 9.
Write at least five form of energy.
Answer:
Mechanical energy i.e. (K.E + P.E), heat energy, chemical energy, atomic energy, wind energy.
Question 10.
What do you mean by potential energy? Explain with example.
Answer:
The energy which a body possess due to its position or due to change in the shape is called potential energy.
Example 1: A brick which is suspended above the ground has energy because it would do work by falling to the ground. Its energy is due to its position and therefore it is potential energy.
Example 2: The potential energy of a stretched bow string results from a change in its shape.
Work and Energy Short Answer Type Questions
Question 1.
What is bio-mass energy? What are its uses?
Answer:
The excreta of animals, cow dug, wild plants and dry leaves of plants are fermented in a digestive tank. The produced gas is called bio gas/Gobar gas which is known as bio mass energy. This gas bums with smokless flame. Therefore it is a non polluting gas. This is used as a house fuel and for lighting the house. ‘
Question 2.
Define the following terms:
- Ocean energy
- Atomic energy
Answer:
- The energy generated by tides, (low/high), prompt waves etc. in an ocean is known as ocean energy. This energy is converted into electrical energy.
- The energy obtained by the division or fusion of nucleus is known as atomic energy. The electricity is generated from atomic (nuclear) reactor.
Question 3.
- Define work. Give its S.I unit. Write an expression for positive work done.
- Calculate the work done in pushing a cart through a distance of 50 m against the force of friction equal to 250 N. Also state the type of work done..
- What will be the work done, if displacement of the object is perpendicular to the directions of force.
- When person moves on a circular path and reached to the same point from where he starts, then what will be the work done?
Answer:
- Work is said to be done when the force applied on an object produces a displacement in the object in the direction of force applied.
Work = Force x displacement (positive work)
S.I unit of work done = Joule. - We are given that
Force (F) = 250 N, displacement (s) = 50 w
∴ Work done = F x S
= 250 x 50
= 1250 Joule
Here, work done is negative. - The work done by force is zero.
- The work done is also zero here because there is no displacement.
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