Assertion and Reason Questions for Class 9 Science Chapter 11 Work and Energy

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Directions: In the following questions, a statement of assertion (A) is followed by a statement of reason (R). Mark the correct choice as:
(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.

Q.1. 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.

Answer Answer: (c)

Q.2. Assertion : The work done during a round trip is not zero.
Reason : No force is required to move a body in its round trip.

Answer Answer: (d)

Q.3. 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.

Answer Answer: (b)

Q.4. Assertion : The kinetic energy, with any reference, must be positive.
Reason : In the expression for kinetic energy, the velocity appears with power 2 and mass is a scalar quantity.

Answer Answer: (a)

Q.5. Assertion : A crane P lifts a car upto a certain height in 1 min. Another crane Q lifts the same car upto the same height in 2 min. Then crane P consumes two times more fuel than crane Q.
Reason : Crane P supplies two times more power than crane Q.

Answer Answer: (a)

Q.6. Assertion : Watt hour has units of energy.
Reason : Kilowatt hour (kW h) is the unit of electric power.

Answer Answer: (c)

Q.7. 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.

Answer Answer: (d)

Q.8. 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.

Answer Answer: (a)

Q.9. 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.

Answer Answer: (b)

Q.10. Assertion : According to law of conservation of mechanical energy, change in potential energy is equal and opposite to the change in kinetic energy.
Reason : Mechanical energy is not a conserved quantity.

Answer Answer: (c)

Q.11. Assertion : A winded toy car, when placed on floor, starts moving.
Reason : Toy car has kinetic energy stored in it which facilitates its motion.

Answer Answer: (c)

Q.12. 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.

Answer Answer: (a)

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