# NCERT Exemplar Class 11 Physics Chapter 5 Work, Energy and Power

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## 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 not 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

(b) the magnetic forces do not work on each particle

## Q.2. 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

(c) Total mechanical energy

## Q.3. Two inclined ffictionless 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 figure.

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.

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

## Q.4. 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

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

(a) +2000 J
(b) -200 J
(c) zero
(d) -20,000 J

(c) zero

## Q.6. 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

(d) at first greater than mg and later becomes equal to mg

## Q.7. 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

(c) Total linear momentum

(a) V=0,K = E
(b) V=E,K=0
(c) V< E, K= O
(d) V= 0,K<E

(b)

(b)

(b)

(d)

(c)

(b)

(b)

## Q.15. A man of mass m, standing at the bottom of the staircase, of height L climbs it and stands at its top.

(a) Work done by all forces on man is equal to the rise in potential energy mgL.
(b) Work done by all forces on man is zero.
(c) Work done by the gravitational force on man is mgL.
(d) The reaction force from a step does not do work because the point of application of the force does not move while the force exists.

(b) (d)

## Q.16. A bullet of mass m fired at 30° to the horizontal leaves the barrel of the gun with a velocity v. The bullet hits a soft target at a height h above the ground while it is moving downward and emerge out with half the kinetic energy it had before hitting the target.

Which of the following statements are correct in respect of bullet after it emerges out of the target?

(a) The velocity of the bullet will be reduced to half its initial value.
(b) The velocity of the bullet will be more than half of its earlier velocity
(c) The bullet will continue to move along the same parabolic path.
(d) The bullet will move in a different parabolic path.
(e) The bullet will fall vertically downward after hitting the target.
(f) The internal energy of the particles of the target will increase.

(b) (d) (f)

### NCERT Exemplar Class 11 Physics Solutions

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