• Skip to main content
  • Skip to secondary menu
  • Skip to primary sidebar
  • Skip to footer

CBSE Tuts

CBSE Maths notes, CBSE physics notes, CBSE chemistry notes

  • NCERT Solutions
    • NCERT Solutions for Class 12 English Flamingo and Vistas
    • NCERT Solutions for Class 11 English
    • NCERT Solutions for Class 11 Hindi
    • NCERT Solutions for Class 12 Hindi
    • NCERT Books Free Download
  • TS Grewal
    • TS Grewal Class 12 Accountancy Solutions
    • TS Grewal Class 11 Accountancy Solutions
  • CBSE Sample Papers
  • NCERT Exemplar Problems
  • English Grammar
    • Wordfeud Cheat
  • MCQ Questions

NCERT Exemplar Problems Class 9 Science – Work and Energy

NCERT Exemplar Problems Class 9 Science – Work and Energy

Multiple Choice Questions (MCQs)

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:
(c)
Since, total energy of the system is always conserved, so when a body falls freely towards the earth, then its total energy remains constant i.e., the sum of the potential energy and kinetic energy of the body would be same at all points.

You can also Download NCERT Exemplar Class 9 Science Solutions to help you to revise complete Syllabus and score more marks in your examinations.

Question 2:
A car is accelerated on a lavelled 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:
(a)
Potential energy of the car don’t change and kinetic energy changes by as follows
NCERT Exemplar Problems Class 9 Science - Work and Energy Img 1
So in this process, the kinetic energy of car becomes 16 times that of initial energy.

Question 3:
In case of negative work, the angle between the force and displacement is
(a) 0                     (b) 45°                        (c) 90°                        (d) 180°
Answer:
(d) (a) Work done W = F.d cos 0
∴Work done at θ= 0°, W = F.d cos 0°                                                (∴cos0° = 1)
=>                               W = F.d
For angle θ = 0°,
Work done Is positive, so it is not true.
(b) We know that work done, W = F .d cos 0
NCERT Exemplar Problems Class 9 Science - Work and Energy Img 2
For angle 0 = 45°,
work done is positive, so it is not true.
(c) We know that work done, W = d cos θ
Work done at θ = 90°,      W = F.d cos 90°                                      (∴cos 90° = 0)
W = 0
So, it is not true.
(d) Work done at θ = 180°, W = F.d cosθ (∴ cos 180°= -1)
W = -F. d
For negative work, the angle between the force and displacement should be 180°. (/.e„ force and displacement are antiparallel to each other) So, it is true.

Question 4:
An iron sphere of mass 10 kg has the same diameter as an aluminium sphere of mass 3.5 kg. Both spheres are dropped simultaneously from a tower. When they are 10 m above the ground, they have the same
(a) acceleration                                          (b) momenta
(c) potential energy                                   (d) kinetic energy
Answer:
(a) When both spheres are dropped simultaneously from a tower, they have same acceleration. Because, during free fall acceleration of body becomes equals to (g = 9.8 m/s2) and ‘g’ depends on mass of earth and radius of earth
NCERT Exemplar Problems Class 9 Science - Work and Energy Img 3

Question 5:
A girl is carrying a school bag of 3 kg mass on her back and moves 200 m on a lavelled road. The work done against the gravitational force will be (9 = 10 ms−2)
(a) 6 x 103 J                                   (b) 6 J                        (c) 0.6 J                     (d) zero
Answer:
(d)
We know that, work done = F . d cos 0
Force on school bag makes an angle 90° from the road.
NCERT Exemplar Problems Class 9 Science - Work and Energy Img 4
i.e.,      0 = 90°
W = F . d cos 90°       (∴ cos 90° = 0°)
W = 0
Flence, work done against the gravitational force is 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:
(c) We know that, joule, newton metre and kilowatt hour are the units of energy and the kilowatt is the unit of power.

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:
(d)
We know that, W = F.d cos 0
Here, F = force applied on the object, d = displacement and 0 is angle between force and displacement. So, the work done on an object does not depend upon the 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:
(d) Potential energy is stored energy or the energy of position, so water stored fn a dam possesses potential energy.

Free online gravitational potential energy calculator is used to calculate the potential energy quickly.

Question 9:
A body is falling from a height h. 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) more kinetic and less potential energy
Answer:
(c)

NCERT Exemplar Problems Class 9 Science - Work and Energy Img 5

Short Answer Type Questions

Question 10:
A rocket is moving up with a velocity v. If the velocity of this rocket is suddenly tripled, what will be the ratio of two kinetic energies?
Answer:
NCERT Exemplar Problems Class 9 Science - Work and Energy Img 6

Question 11:
Avinash can run with a speed of 8 ms-1 against the frictional force of 10 N and Kapil can move with a speed of 3 ms-1 against the frictional force of 25 N. Who is more powerful and why?
Answer:
Given, force applied by Avinash = 10 N
Speed of Avinash = 8 ms-1                                               ‘
Power of Avinash = F.v = 10×8 = 80W
Now, force applied by Kapil = 25 N
Speed of Kapil = 3ms-1
Power of Kapil = Fv = 25×3 = 75W
Since, Avinash has more power (80 – 75) = 5 W than Kapil. So, Avinash is more powerful.

Question 12:
A boy is moving on a straight road against a frictional force of 5 N. After travelling a distance of 1.5 km, he forgot the correct path at a round about of radius 100 m as shown in figure. However, he moves on the circular path for one and half cycle and then he moves forward upto 2.0 km. Calculate the work done by him.
NCERT Exemplar Problems Class 9 Science - Work and Energy Img 7

Answer:
Given, force applied by boy against friction = 5 N
Displacement on the circular path = One cycle + Half cycled = 0 + Half cycle
= 0 + Diameter of circular path (∴Displacement depends on initial and final point)
= 0+ 2r = 0+2×100             [∴r = 100m]
= 0 + 200 = 200 m
∴ Total displacements = 1.5 km + 200 m + 2.0 km
= 1.5 x 1000 + 200 + 2 x 1000km                          (1 km= 1000 m)
= 3700 m
Work done by boy = F . s cos θ
= 5 x 3700 x cos 0 = 18500 J

Question 13:
Can any object have mechanical energy even if its momentum is zero?
Answer:
Since, mechanical energy is the sum of kinetic energy and potential energy.
And as given that, momentum of the body is zero, it means velocity of the body is zero, so it has kinetic energy equals to zero. But it may have potential energy.
So, even if the momentum of the body is zero, it may have mechanical energy.

Question 14:
Can any object have momentum even if its mechanical energy is zero? Explain.
Answer:
Since, mechanical energy = potential energy + kinetic energy
If mechanical energy = 0
So,      PE+ KE= 0

⇒           PE=-KE
So, we can say that body may have momentum, in case mechanical energy is zero

Question 15:
The power of a motor pump is 2 kW. How much water per minute, the pump can raise to a height of 10 m? [given, g = 10 ms-2]
Answer :
NCERT Exemplar Problems Class 9 Science - Work and Energy Img 8
Question 16:
The weight of a person on a planet A is about half that on the earth. He can jump upto 0.4 m height on the surface of the earth. How high he can jump on the planet A?
Answer:
It is given that weight of person on the earth = w                                                         {i.e.,w = mg)
And as he can jump upto height (h, = 0.4m)
So, potential energy at this point = mgh = mg x .04                                                          …(i)
And it is given that
NCERT Exemplar Problems Class 9 Science - Work and Energy Img 9
NCERT Exemplar Problems Class 9 Science - Work and Energy Img 10

Question 17:
The velocity of a body moving in a straight line is increased by applying a constant force F, for some distance in the direction of the motion. Prove that the increase in the kinetic energy of the body is equal to the work done by the force on the body.
Answer:
Consider an object of mass m moving with a uniform velocity u.
Let, it now be displaced through a distance s, when a constant force F acts on it in the direction of its displacement.
From the third equation of motion,
v2 = u2 + 2as
v2 – u2 = 2as
NCERT Exemplar Problems Class 9 Science - Work and Energy Img 11
It is clear that the work done is equal to the change in the kinetic energy of an object.

Question 18:
Is it possible that an object is in the state of accelerated motion due to external force acting on it, but no work is being done by the force? Explain it with an example.
Answer:
Yes, when force acts in a direction perpendicular to the direction of displacement.
NCERT Exemplar Problems Class 9 Science - Work and Energy Img 12
e.g., earth revolves around the sun under gravitational force of sun on earth, but no work is done by the sun, though earth has centripetal acceleration.

Question 19:
A ball is dropped from a height of 10 m. If the energy of the ball reduces by 40% after striking the ground, how much high can the ball bounce back? [g – 10 ms-2]
Answer:
If the energy of the ball reduces by 40% after striking the ground, then remaining energy of the ball will
be 60% of initial energy.
Let initial energy of the body of mass (m) at height(h) is (mgh).
According to the question, mgh’ = 60% of mgh              [given,h = 10m and g = 10ms-2]
NCERT Exemplar Problems Class 9 Science - Work and Energy Img 13

Question 20:
If an electric iron of 1200 W is used for 30 min everyday, find electric energy consumed in the month of April.
Answer:
NCERT Exemplar Problems Class 9 Science - Work and Energy Img 14

Long Answer Type Questions

Question 21:
A light and a heavy object have the same momentum. Find out the ratio of their kinetic energies. Which one has a larger kinetic energy?
Answer:
NCERT Exemplar Problems Class 9 Science - Work and Energy Img 15

Question 22:
An automobile engine propels a 1000 kg car A along a lavelled road at a speed of 36 kmh-1. Find the power if the opposing frictional force is 100 N. Now, suppose after travelling a distance of 200 m, this car collides with another stationary car B of same mass and comes to rest. Let its engine also stop at the same time. Now car B starts moving on the same level road without getting its engine started. Find the speed of the car 6 just after the collision.
Answer:
NCERT Exemplar Problems Class 9 Science - Work and Energy Img 16
NCERT Exemplar Problems Class 9 Science - Work and Energy Img 17

Question 23:
A girl having mass of 35 kg sits on a trolley of mass 5 kg. The trolley is given an initial velocity of 4 ms-1 by appling a force. The trolley comes to rest after traversing a distance of 16 m. (a) How much work is done on the trolley? (b) How much work is done by the girl?
Answer:
NCERT Exemplar Problems Class 9 Science - Work and Energy Img 18

Question 24:
Four men lift a 250 kg box to a height of 1 m and hold it without raising or lowering it. (a) How much work is done by the men in lifting the box? (b) How much work do they do in just holding it? (c) Why do they get tired while holding it? [given = 10 ms-2].
Answer:
Given, m = 250kg, height (h) = 1 m and acceleration due to gravity g = 10 ms-2
(a) Work done by the man in lifting the box
W = Potential energy of box W = mgh
W = 250 x 1×10= 2500 J
(b) Work done is zero in holding a box, because displacement is zero.
(c) In holding the box, the energy of man loses. Due to loss of energy he felt tired.

Question 25:
What is power? How do you differentiate kilowatt from kilowatt hour? The Jog Falls in Karnataka state are nearly 20 m high. 2000 tonnes of water falls from it in a minute. Calculate the equivalent power if all this energy can be utilised? [g= 10 ms-2]
Answer:
(i) Power is defined as the rate of doing work or the rate of transfer of energy. The unit of . power is watt or kilowatt.            [1 kW= 1000W]
(ii) Kilowatt is the unit of power while kilowatt hour is bigger unit of energy
1 kWh = 1000 x 3600 ⇒ 1 kilowatt hour = 3.6x 106 J
NCERT Exemplar Problems Class 9 Science - Work and Energy Img 19

Question 26:
How is the power related to the speed at which a body can be lifted? How many kilograms will a man working at the power of 100 W, be able to lift at constant speed of 1 ms-1 vertically? [g – 10 ms-2]
Answer:
NCERT Exemplar Problems Class 9 Science - Work and Energy Img 20

Question 27:
Define watt. Express kilowatt in terms of joule per second. A 150 kg car engine develops 500 W for each kg. What force does it exert in moving the car at speed of 20 ms-1?
Answer:
NCERT Exemplar Problems Class 9 Science - Work and Energy Img 21

NCERT Exemplar ProblemsNCERT Exemplar MathsNCERT Exemplar Science

Primary Sidebar

NCERT Exemplar problems With Solutions CBSE Previous Year Questions with Solutoins CBSE Sample Papers
  • The Summer Of The Beautiful White Horse Answers
  • Job Application Letter class 12 Samples
  • Science Lab Manual Class 9
  • Letter to The Editor Class 12 Samples
  • Unseen Passage For Class 6 Answers
  • NCERT Solutions for Class 12 Hindi Core
  • Invitation and Replies Class 12 Examples
  • Advertisement Writing Class 11 Examples
  • Lab Manual Class 10 Science

Recent Posts

  • Understanding Diversity Question Answer Class 6 Social Science Civics Chapter 1 NCERT Solutions
  • Our Changing Earth Question Answer Class 7 Social Science Geography Chapter 3 NCERT Solutions
  • Inside Our Earth Question Answer Class 7 Social Science Geography Chapter 2 NCERT Solutions
  • Rulers and Buildings Question Answer Class 7 Social Science History Chapter 5 NCERT Solutions
  • On Equality Question Answer Class 7 Social Science Civics Chapter 1 NCERT Solutions
  • Role of the Government in Health Question Answer Class 7 Social Science Civics Chapter 2 NCERT Solutions
  • Vital Villages, Thriving Towns Question Answer Class 6 Social Science History Chapter 9 NCERT Solutions
  • New Empires and Kingdoms Question Answer Class 6 Social Science History Chapter 11 NCERT Solutions
  • The Delhi Sultans Question Answer Class 7 Social Science History Chapter 3 NCERT Solutions
  • The Mughal Empire Question Answer Class 7 Social Science History Chapter 4 NCERT Solutions
  • India: Climate Vegetation and Wildlife Question Answer Class 6 Social Science Geography Chapter 8 NCERT Solutions
  • Traders, Kings and Pilgrims Question Answer Class 6 Social Science History Chapter 10 NCERT Solutions
  • Environment Question Answer Class 7 Social Science Geography Chapter 1 NCERT Solutions
  • Understanding Advertising Question Answer Class 7 Social Science Civics Chapter 7 NCERT Solutions
  • The Making of Regional Cultures Question Answer Class 7 Social Science History Chapter 9 NCERT Solutions

Footer

Maths NCERT Solutions

NCERT Solutions for Class 12 Maths
NCERT Solutions for Class 11 Maths
NCERT Solutions for Class 10 Maths
NCERT Solutions for Class 9 Maths
NCERT Solutions for Class 8 Maths
NCERT Solutions for Class 7 Maths
NCERT Solutions for Class 6 Maths

SCIENCE NCERT SOLUTIONS

NCERT Solutions for Class 12 Physics
NCERT Solutions for Class 12 Chemistry
NCERT Solutions for Class 11 Physics
NCERT Solutions for Class 11 Chemistry
NCERT Solutions for Class 10 Science
NCERT Solutions for Class 9 Science
NCERT Solutions for Class 7 Science
MCQ Questions NCERT Solutions
CBSE Sample Papers
NCERT Exemplar Solutions LCM and GCF Calculator
TS Grewal Accountancy Class 12 Solutions
TS Grewal Accountancy Class 11 Solutions