# NCERT Physics Class 11 Exemplar Ch 6 Work Energy and Power Part 1

## MCQ I

Q 1. An electron and a proton are moving under the influence of mutual forces. In calculating the change in the kinetic energy of the system during motion, one ignores the magnetic force of one on another. This is because,

(a) The two magnetic forces are equal and opposite, so they produce no net effect.

(b) The magnetic forces do no work on each particle.

(c) The magnetic forces do equal and opposite (but non-zero) work on each particle.

(d) The magnetic forces are necessarily negligible.

Ans:

(b)

Q 2. A proton is kept at rest. A positively charged particle is released from rest at a distance d in its field. Consider two experiments; one in which the charged particle is also a proton and in another, a positron. In the same time t, the work done on the two moving charged particles is

(a) Same as the same force law is involved in the two experiments.

(b) Less for the case of a positron, as the positron moves away more rapidly and the force on it weakens.

(c) More for the case of a positron, as the positron moves away a larger distance.

(d) Same as the work done by charged particle on the stationary proton.

Ans: (c)

Q 3. A man squatting on the ground gets straight up and stand. The force of reaction of ground on the man during the process is

(a) Constant and equal to mg in magnitude.

(b) Constant and greater than mg in magnitude.

(c) Variable but always greater than mg.

(d) At first greater than mg, and later becomes equal to mg.

Ans: (d)

Q 4. A bicyclist comes to a skidding stop in 10 m. During this process, the force on the bicycle due to the road is 200N and is directly opposed to the motion. The work done by the cycle on the road is

(a)

(b)

(c) Zero

(d)

Ans: (c)

Q 5. A body is falling freely under the action of gravity alone in vacuum. Which of the following quantities remain constant during the fall?

(a) Kinetic energy.

(b) Potential energy.

(c) Total mechanical energy.

(d) Total linear momentum.

Ans: (c)

Q 6. During inelastic collision between two bodies, which of the following quantities always remain conserved?

(a) Total kinetic energy.

(b) Total mechanical energy.

(c) Total linear momentum.

(d) Speed of each body.

Ans: (c)

Q 7. Two inclined frictionless tracks, one gradual and the other steep meet at A from where two stones are allowed to slide down from rest, one on each track as shown in Fig.

Which of the following statement is correct?

(a) Both the stones reach the bottom at the same time but not with the same speed.

(b) Both the stones reach the bottom with the same speed and stone I reaches the bottom earlier than stone II.

(c) Both the stones reach the bottom with the same speed and stone II reaches the bottom earlier than stone I.

(d) Both the stones reach the bottom at different times and with different speeds.

Ans: (c)

Q 8. The potential energy function for a particle executing linear SHM is given by where k is the force constant of the oscillator. For k = 0.5N/m, the graph of versus x is shown in the figure. A particle of total energy E turns back when it reaches. If V and K indicate the P.E. and K.E., respectively of the particle at, then which of the following is correct?

(a)

(b)

(c)

(d)

Ans: (b)

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