CBSE Class 9 Science Work and Energy MCQs Set 03

Question. A stretched spring possesses
(a) kinetic energy
(b) elastic potential energy
(c) electrical energy
(d) magnetic energy

Answer: b

Question. Kinetic energy of a body depends
(a) on its mass only
(b) on its velocity only
(c) on its mass as well as on its velocity
(d) neither on its mass nor on its velocity

Answer: c

Question. One kilowatt is approximately equal to
(a) 1.34 hp
(b) 1.56 hp
(c) 2.50 hp
(d) 1.83 hp

Answer: a

Question. Two boys A and B lift 100 bricks through the same height in 5 minutes and 6 minutes respectively. Then
(a) A has more power than B
(b) B has more power than A
(c) both have same power
(d) data insufficient

Answer: a

Question. A rocket rises up in air due to the force generated by the fuel. The work done by the
(a) fuel is negative work and by force of gravity is positive work
(b) fuel is positive work and by force of gravity is negative work
(c) both fuel and force of gravity do positive work
(d) both fuel and force of gravity do negative work

Answer: b

Question. If a body is raised through height h on the surface of earth and the energy spent is E , then for the same amount of energy the body on the surface of moon will rise through the height of
(a) 2h
(b) 6h
(c) 4h
(d) 12h

Answer: b

Question. A boy has four options to move a body through 3m as indicated below
(a) Push over an inclined plane
(b) lift vertically upwards
(c) Push over smooth rollers
(d) Push on a plane horizontal surface. In which case is maximum work done?

Answer: b

Question. In an electric flashlight the chemical energy of the cell is
(a) converted into heat energy only
(b) converted into light energy only
(c) converted first into light and then heat energy
(d) converted first into heat and then light energy

Answer: d

Question. Which of the following is not an example of potential energy?
(a) Water stored in a dam.
(b) A stretched bow and arrow system.
(c) A dog chasing a hare.
(d) A stone lying on the top of a roof.

Answer: c

Question. In which of the following cases is the potential energy of a spring minimum?
(a) When it is compressed
(b) When it is extended
(c) When it is at its natural length
(d) When it is at its natural length but is kept at a height h above the ground.

Answer: c

Question. Which of the following statements is correct regarding the relation between centripetal force and radius of the circular path?
(a) The work done by the centripetal force increases if the radius of the path is increased
(b) The work done by the centripetal force decreases by decreasing the radius
(c) The work done by the centripetal force increases by decreasing the radius
(d) The work done is always zero.

Answer: d

Question. A man carrying a bucket of water and walking on a rough level road with a uniform velocity does no work while carrying the bucket. Which of the following statements gives the correct reason for this?
(a) The displacement of the bucket is zero.
(b) There is no force acting on the bucket.
(c) The displacement of the bucket is in the direction of force applied.
(d) There is no displacement in the direction of the force applied.

Answer: d

Question. Which of the following statements is true about work done?
1. Work done by a force is always positive.
2. SI unit of work is joule.
3. Work has both, magnitude and direction.
4. Work is said to be done if an object is displaced when a force acts on it.
(a) 1 and 2
(b) 2 and 3
(c) 2 and 4
(d) 1, 2, 3 and 4

Answer: c

Question. A rocket rises up vertically. What happens to its potential energy?
(a) It increases.
(b) It initially increases then decreases.
(c) It initially decreases then increases.
(d) It increases, till it becomes maximum.

Answer: d

FILL IN THE BLANK

Question. Two bodies of masses m1 and m2 have equal moments. Their kinetic energies are in the ratio.
Answer: m2/m1

Question. A truck and a car moving with the same kinetic energy are brought to rest by the application of brakes which provide equal retarding forces. The distance moved by the truck, in coming to rest, will then be _____ the distance moved by car.
Answer: the same

Question. One horse power = _____ watt.
Answer: 746

Question. _____ energy can never be negative
Answer: kinetic

Question. An electric motor exerts a force of 40N on a cable and pulls it through a distance of 30m in one minute. the power supplied by the motor in watts is _____
Answer: 20

Question. The work done in holding 15 kg suitcase while waiting for a bus for 15 minute is _____
Answer: zero

Question. A one kilogram mass has a kinetic energy of one joule when its speed is _____ meter/sec.
Answer: √2

TRUE/FALSE

Question. Work done by conservative forces is equal to increase in potential energy.
Answer: False

Question. Kinetic energy of a body depends upon the direction of motion.
Answer: False

Question. Work done by friction can-never be positive.
Answer: False

Question. Gravitational force is non-conservative.
Answer: False

Question. Work done by conservative force in round trip is zero.
Answer: True

Question. A body cannot have momentum when its energy is zero.
Answer: True

Question. A man carrying a bucket of water, walking on a level road with a uniform velocity does no work.
Answer: True

ASSERTION AND REASON

Question. Assertion : Work done by the gravitational force through a certain distance is constant irrespective of the fact that the body has a uniform or accelerated motion.
Reason : Gravitational force is a conservative force.
Options:
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true.

Answer: b

Question. Assertion : Work done by or against gravitational force in moving a body from one point to another is independent of the actual path followed between the two points.
Reason : Gravitational forces are conservative forces.
Options:
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true.

Answer: a

Question. Assertion : The work done during a round trip is always zero.
Reason : No force is required to move a body in its round trip.
Options:
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true.

Answer: a

Question. Assertion : No work is done when a woman carrying a load on her head, walks on a level road with a uniform velocity.
Reason : No work is done if force is perpendicular to the direction of displacement.
Options:
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true.

Answer: a

Question. Assertion : When the force retards the motion of a body, the work done is negative.
Reason : Work done depends on angle between force and displacement.
Options:
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true.

Answer: b

Question. Assertion : The work done during a round trip is always zero.
Reason : No force is required to move a body in its round trip.
Options:
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true.

Answer: d

Question. Assertion : A spring has potential energy, both when it is compressed or stretched.
Reason : In compressing or stretching, work is done on the spring against the restoring force.
Options:
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true.

Answer: a

Question. Assertion : The change in kinetic energy of a particle is equal to the work done on it by the net force.
Reason : Change in kinetic energy of particle is equal to the work done only in case of a system of one particle.
Options:
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true.

Answer: c

Question. Assertion : Work done by or against gravitational force in moving a body from one point to another is independent of the actual path followed between the two points.
Reason : Gravitational forces are conservative forces.
Options:
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true.

Answer: a

Question. Assertion : A light body and heavy body have same momentum. Then they also have same kinetic energy.
Reason : Kinetic energy depends on mass of the body.
Options:
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true.

Answer: d