JEE Advanced (Assertion-Reason Type): Work, Power & Energy | Chapter-wise Tests for JEE Main & Advanced PDF Download

Directions : Each of these questions contain two statements, Assertion and Reason. Each of these questions also has alternative choices, only one of which is the correct answer.
Q.1. Assertion : A work done by friction is always negative.
Reason : If frictional force acts on a body its K.E. may decrease.
(a) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
(b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(c) Assertion is correct, reason is incorrect
(d) Assertion is incorrect, reason is correct.

Correct Answer is option (d)
When frictional force is opposite to velocity, kinetic energy will decrease.

Q.2. Assertion : A man rowing a boat upstream is at rest with respect to the bank. He is doing no external work.
Reason : Work done by constant force, W = F s cosθ.
(a) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
(b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(c) Assertion is correct, reason is incorrect
(d) Assertion is incorrect, reason is correct.

Correct Answer is option (a)
In this case, s = 0, and so W = 0.

Q.3. Assertion : The work done in moving a body over a closed loop is zero for every force in nature.
Reason : Work done depends on nature of force.
(a) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
(b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(c) Assertion is correct, reason is incorrect
(d) Assertion is incorrect, reason is correct.

Correct Answer is option (b)
In close loop, s = 0, and so W = Fs = 0.

Q.4. 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 work done only in case of a system of one particle.

(a) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
(b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(c) Assertion is correct, reason is incorrect
(d) Assertion is incorrect, reason is correct.

Correct Answer is option (c)
Change in kinetic energy = work done by net force. This relationship is valid for particle as well as system of particles.

Q.5. Assertion: Kinetic energy of a system can be increased or decreased without applying any external force on the system.
Reason: This is because K.E. = mV²/2, so it independent of any external forces.
(a) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
(b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(c) Assertion is correct, reason is incorrect
(d) Assertion is incorrect, reason is correct.

Correct Answer is option (c)
K.E. can be increased or decreased without applying any external force, as internal forces can do work e.g., explosion of a bomb.

Q.6. Assertion: The work done during a round trip is always zero.
Reason: No force is required to move a body in its round trip.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (d)
In a round trip work done is zero only when the force is conservative in nature.  Force is always required to move a body in a conservative or non-conservative field.

Q.7. Assertion: Work done by friction on a body sliding down an inclined plane is positive.
Reason: Work done is greater than zero, if angle between force and displacement is acute or both are in same direction.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (e)
When a body slides down on inclined plane, work done by friction is negative because it opposes the motion (θ = 180° between force and displacement) If θ < 90^∘ then W = positive because W = F.s.cos θ.

Q.8. Assertion: The instantaneous power of an agent is measured as the dot product of instantaneous velocity and the force acting on it at that instant.
Reason: The unit of instantaneous power is watt.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (b)
and unit of power is Watt.

Q.9. 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.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (c)
Change in kinetic energy = work done by net force. This relationship is valid for particle as well as system of particles.

Q.10. 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.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (a)
The work done on the spring against the restoring force is stored as potential energy in both conditions when it is compressed or stretched.

Q.11. Assertion: Comets move around the sun in elliptical orbits. The gravitational force on the comet due to sun is not normal to the comet's velocity but the work done by the gravitational force over every complete orbit of the comet is zero.
Reason: Gravitational force is a non conservative force.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (c)
The gravitational force on the comet due to the sun is a conservative force. Since the work done by a conservative force over a closed path is always zero (irrespective of the nature of path), the work done by the gravitational forces over every complete orbit of the comet is zero.

Q.12. Assertion: The rate of change of total momentum of a many particle system is proportional to the sum of the internal forces of the system.
Reason: Internal forces can change the kinetic energy but not the momentum of the system.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (e)
Rate of change of momentum is proportional to external forces acting on the system. The total momentum of whole system remain constant when no external force is acted upon it. Internal forces can change the kinetic energy of the system.

Q.13. Assertion: Water at the foot of the water fall is always at different temperature from that at the top.
Reason: The potential energy of water at the top is converted into heat energy during falling.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (a)
When the water is at the top of the fall it has potential energy mgh (where m is the mass of the water and h is the height of the fall). On falling, this potential energy is converted into kinetic energy, which further converted into heat energy and so temperature of water increases.

Q.14. Assertion: The power of a pump which raises 100 kg of water in 10sec to a height of 100 m is 10 KW.
Reason: The practical unit of power is horse power.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (b)
The power of the pump is the work done by it per sec. Power = work /time = mgh/t
= = 10⁴W = 10kW. Also 1 Horse power (hp) =746 W.

Q.15. Assertion: When the force retards the motion of a body, the work done is zero.
Reason: Work done depends on angle between force and displacement.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (e)
When the force retards the motion, the work done is negative. Work done depends on the angle between force and displacement W = Fs cos θ

Q.16. Assertion: In an elastic collision of two bodies, the momentum and energy of each body is conserved.
Reason: If two bodies stick to each other, after colliding, the collision is said to be perfectly elastic.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (d)
In an elastic collision both the momentum and kinetic energy remains conserved. But this rule is not for individual bodies, but for the system of bodies before and after the collision. While collision in which there occurs some loss of kinetic energy is called inelastic collision. Collision in daily life are generally inelastic. The collision is said to be perfectly inelastic, if two bodies stick to each other.

Q.17. Assertion: A body cannot have energy without having momentum but it can have momentum without having energy.
Reason: Momentum and energy have same dimensions.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (d)
A body can have energy without having momentum if it possess potential energy but if body possess momentum then it must posses kinetic energy. Momentum and energy have different dimensions.

Q.18. Assertion: Power developed in circular motion is always zero.
Reason: Work done in case of circular motion is zero.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

 Correct Answer is option (e)
Work done and power developed is zero in uniform circular motion only.

Q.19. Assertion: A quick collision between two bodies is more violent than slow collision, even when initial and final velocities are identical.
Reason: The rate of change of momentum determine that force is small or large.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (a)
In a quick collision, time t is small. As F × t = constant, therefore, force involved is large, i.e. collision is more violent in comparison to slow collision.

Q.20. 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.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Correct Answer is option (a)
From, definition, work done in moving a body against a conservative force is independent of the path followed.