Assertion (A): Karnam Malleshwari famous Indian weight lifter lifts a weight up and returns it to same initial position along the same path. Net work done by muscles of weight lifter is positive.
Reason (R): Net displacement of weight is zero.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Reason (R) is true as the weight returns to its starting point, making net displacement zero.
Assertion (A) is considered true in a physiological sense, as muscles expend energy. However, zero net displacement (R) implies zero net mechanical work on the weight by gravity, and thus zero net mechanical work by muscles if there is no change in kinetic energy. Therefore, (R) does not explain (A).
Assertion (A): If in a round trip work done by a force is zero then force is conservative.
Reason (R): Work done by conservative force field is independent of path.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Assertion (A) states the definition of a conservative force: the work done in a closed loop is zero.
Reason (R) states a key property of conservative forces: their work is path-independent. Path independence directly implies that the work done in any round trip (closed path) is zero, thus (R) correctly explains (A).
Assertion (A): A body cannot have kinetic energy without having linear momentum but it can have momentum without having mechanical energy.
Reason (R): Linear momentum and energy have same dimensions.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Assertion (A) is false:
If a body has linear momentum (\(p \neq 0\)), it must have velocity (\(v \neq 0\)), which implies it must also have kinetic energy (\(KE = \frac{1}{2}mv^2 \neq 0\)). Since kinetic energy is a component of mechanical energy, it cannot have momentum without mechanical energy.
Reason (R) is false: Linear momentum has dimensions \(MLT^{-1}\) while energy has dimensions \(ML^2T^{-2}\), which are different.
Assertion (A): A spring has potential energy, both when it is compressed or elongated.
Reason (R): In compressing or stretching, work is done on the spring against the restoring force.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Assertion (A) is true:
A spring stores elastic potential energy, calculated as \(U = \frac{1}{2}kx^2\), when it is compressed or stretched from its equilibrium position.
Reason (R) is true: This potential energy is stored because an external force does work against the spring's restoring force during deformation. Reason (R) correctly explains Assertion (A).
Assertion (A): There is no term like instantaneous work similar to instantaneous velocity.
Reason (R): For work to be done, the force must act for a displacement.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Assertion (A) is true: Velocity is a rate of change at an instant, but work \(W = \int F \cdot dr\) fundamentally involves displacement.
Instantaneous power \(P = F \cdot v\) exists, but not instantaneous work.
Reason (R) is true: Work requires a force to act over a non-zero displacement. Reason (R) correctly explains why instantaneous work is not a valid concept.
Assertion (A): A man of mass \(m\), standing on a frictionless surface pushes a wall and acquires a velocity \(v_0\). The work done by the wall on the man is non-zero.
Reason (R): Work done by all the forces is equal to change in kinetic energy.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Assertion (A) is true: The wall exerts a reaction force on the man, which accelerates him to velocity \(v_0\). Since the man undergoes displacement while this force acts, the work done by the wall on the man is positive and non-zero, increasing his kinetic energy. Reason (R) is true: This is the Work-Energy Theorem (\(W_{net} = \Delta KE\)). Reason (R) correctly explains why the work done is non-zero as the man gains kinetic energy.
Assertion (A): Power delivered by all forces acting on a particle moving in a uniform circular motion is always zero.
Reason (R): Work done by all forces acting on a particle moving in a uniform circular motion is zero as KE remains constant.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Assertion (A) is true: In uniform circular motion, the net force (centripetal force) is always perpendicular to the velocity. Power \(P = F \cdot v = |F||v| \cos 90^\circ = 0\). Reason (R) is true: Since speed is constant, kinetic energy \(KE\) is constant, thus \(Delta KE = 0\). By the Work-Energy Theorem, net work done \(W_{net} = \Delta KE = 0\). Reason (R) correctly explains why power is zero.
Assertion (A): Work done by or against force of friction in moving a body in any round trip is always zero.
Reason (R): Frictional force is a conservative force.
1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
View Answer
Frictional force is a non-conservative force. Work done by a non-conservative force over a closed path is generally not zero. Therefore, both Assertion and Reason are false.
Assertion (A): No work is done when an electron completes a circular or an elliptical orbit around the stationary nucleus of an atom.
Reason (R): Electrostatic force is a conservative force.
1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
View Answer
Electrostatic force is a conservative force. For any conservative force, the work done on a particle moving along a closed path is zero. Therefore, both Assertion and Reason are true, and Reason is the correct explanation of the Assertion.
Assertion (A): A man carrying a load on his head and walking with uniform velocity on a street does not work against gravity.
Reason (R): When a body moves with uniform velocity, work done by all forces on this body is zero.
1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
View Answer
Assertion (A) is true because the displacement (horizontal) is perpendicular to the gravitational force (vertical), so work done \(W = \vec{F} \cdot \vec{d} = Fd \cos(90^{circ}) = 0\).
Reason (R) is also true by the Work-Energy Theorem for uniform velocity. However, (R) does not explain (A).