EVENTS CONVENT HIGH SCHOOL
16/12/2021 CLASS- 9 SESSION 2021-22
SUBJECT :SCIENCE
CHAPTER-11
WORK POWER AND ENERGY
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Question 1.
When a body falls freely towards the earth, then its total energy
(a) increases
(b) decreases
(c) remains constant
(d) first increases and then decreases
Answer
Answer: (c) remains constant
Question 2.
A car is accelerated on a levelled road and attains a velocity 4 times of its initial velocity. In this process the potential energy of the car
(a) does not change
(b) becomes twice to that of initial
(c) becomes 4 times that of initial
(d) becomes 16 times that of initial
Answer
Answer: (a) does not change
Question 3.
In case of negative work the angle between the force and displacement is (NCERT Exemplar)
(a) 0°
(b) 45°
(c) 90°
(d) 180°
Answer
Answer: (d) 180°
Kinetic Energy Calculator is a handy tool that solves the kinetic energy problems easily & quickly.
Question 4.
An iron sphere of mass 10 kg has the same diameter as an aluminium sphere of mass is 3.5 kg. Both spheres are dropped simultaneously from a tower. When they are lo m above the ground, they have the same.
(a) acceleration
(b) momenta
(c) potential energy
(d) kinetic energy
Answer
Answer: (a) acceleration
Question 5.
A girl is carrying a school bag of 3 kg mass on her back and moves 200 m on a levelled road. The work done against the gravitational force will be (g = 10 ms²)
(a) 6 × 10³ J
(b) 6 J
(c) 0.6 J
(d) zero
Answer
Answer: (d) zero
Question 6.
Which one of the following is not the unit of energy?
(a) joule
(b) newton metre
(c) kilowatt
(d) kilowatt hour
Answer
Answer: (c) kilowatt
Question 7.
The work done on an object does not depend upon the
(a) displacement
(b) force applied
(c) angle between force and displacement
(d) initial velocity of the object
Answer
Answer: (d) initial velocity of the object
Question 8.
Water stored in a dam possesses
(a) no energy
(b) electrical energy
(c) kinetic energy
(d) potential energy
Answer
Answer: (d) potential energy
Question 9.
A body is falling from a height h. After it has fallen a height
(a) only potential energy
(b) only kinetic energy
(c) half potential and half kinetic energy
(d) more kinetic and less potential energy
Answer
Answer: (c) half potential and half kinetic energy
Question 10.
The number of joules contained in 1 kWh is
(a) 36 × 105 J
(b) 3.6 × 107 J
(c) 36 × 108 J
(d) 3.7 × 107 J
Answer
Answer: (a) 36 × 105 J
Fill in the blanks
1. Work done is product of ………….. and distance moved the direction of the force.
Answer
Answer: force
2. If the angle between force and displacement is …………. then work done is said to be zero.
Answer
Answer: 90°
3. Energy of a body is defined as the capacity or …………. to do work.
Answer
Answer: ability
4. Mechanical energy includes ………….. and ……………
Answer
Answer: kinetic energy, potential energy
5. Energy can neither be ………….. nor ………….. it can only transformed from one form to another.
Answer
Answer: created, destroyed
6. ………….. is defined as the rate of doing work.
Answer
Answer: Power
7. Commercial unit of energy is ………………
Answer
Answer: kilowatt hour
Page 149
Q1. When do we say that work is done?
Work is said to be done when a force causes displacement of an object in the direction of applied force.
Q2. Write an expression for the work done when a force is acting on an object in the direction of its displacement.
Work done = Force x Displacement
Q3. Define 1J of work.
When a force of IN causes a displacement of 1m, in its own direction the work done is said to be one joule.
Q4. A pair of bullocks exerts a force of 140 N on a plough. The field being ploughed is 15 m long. How much work is done in ploughing the length of the field?
Work done = Force x Displacement = 140 x 15 = 2,100 J
Page 156
Q1. What is power?
Power is defined as the rate of doing work
Q2. Define 1 watt of power.
When a work of 1 joule is done in 1 s, the power is said to be one watt.
Q3. A lamp consumes 1000 J of electrical energy in 10 s. What is its power?
Given W = 1000J, t = 10s, P =?
We know, P = W/t = 1000/10 = 100W
Q4. Define average power.
When a machine or person does different amounts of work or uses energy in different intervals of time, the ratio between the total work or energy consumed to the total time is average power.
Q5. A mass of 10 kg is at a point A on a table. It is moved to a point B. If the line joining A and B is horizontal, what is the work done on the object by the gravitational force? Explain your answer.
The work done is zero. This is because the gravitational force and displacement are perpendicular to each other.
Q6. The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
It does not violate the law Of conservation of energy. Whatever, is the decrease in PE due to loss of height, same is the increase in the KE due to increase in velocity of the body.
Q7. What are the various energy transformations that occur when you are riding a bicycle?
The chemical energy of the food changes into heat and then to muscular energy. On paddling, the muscular energy changes into mechanical energy
Q8. Does the transfer of energy take place when you push a huge rock with all your might and fail to move it? Where is the energy you spend going?
Energy transfer does not take place as no displacement takes place in the direction of applied force. The energy spent is used to overcome inertia of rest of the rock.
Match the following columns
| Column A | Column B |
| (a) SI unit of power | (i) 1/2 mv2 |
| (b) Kinetic energy | (ii) The change of one form of energy into another |
| (c) Potential energy | (iii) watt |
| (d) SI unit of work | (iv) If applied force on an object and displacement is in opposite direction. |
| (e) Negative work | (v) Energy possessed by a body due to its position or configuration. |
| (f) Power | (vi) Joule |
| (g) Expression of kinetic energy | (vii) Energy possessed by a body due to its motion. |
| (h) Transformation of energy | (viii) Rate of doing work |
Answer
| Column A | Column B |
| (a) SI unit of power | (iii) watt |
| (b) Kinetic energy | (vii) Energy possessed by a body due to its motion. |
| (c) Potential energy | (v) Energy possessed by a body due to its position or configuration. |
| (d) SI unit of work | (vi) Joule |
| (e) Negative work | (iv) If applied force on an object and displacement is in opposite direction. |
| (f) Power | (viii) Rate of doing work |
| (g) Expression of kinetic energy | (i) 1/2 mv2 |
| (h) Transformation of energy | (ii) The change of one form of energy into another |
