Class 11 Physics Important Chapter 6 Work, Power and Energy

Class 11 Physics Important Chapter 6 Work, Power and Energy Solutions English Medium As Per AHSEC New Syllabus to each chapter is provided in the list so that you can easily browse through different chapters NCERT Class 11 Physics Important Solutions and select need one. AHSEC Class 11 Physics Additional Notes English Medium Download PDF. HS 1st Year Physics Important Solutions in English.

Class 11 Physics Important Chapter 6 Work, Power and Energy

Also, you can read the NCERT book online in these sections Solutions by Expert Teachers as per Central Board of Secondary Education (CBSE) Book guidelines. NCERT Class 11 Physics Additional Question Answer are part of All Subject Solutions. Here we have given HS 1st Year Physics Important Notes in English for All Chapters, You can practice these here.

Work, Power and Energy

Chapter: 6

IMPORTANT QUESTION AND ANSWER

Answer the Following Questions:

1. State the conditions under which a force does no work.

Ans. A force does no work when:

(a) the displacement is zero.

(b) the displacement is perpendicular to the direction of force.

(c) a body moves under the effect of a conservative force over a closed path. 

2. A meteorite burns in the atmosphere before it reaches the earth’s surface. What happens to its momentum?

Ans. The momentum of the meteorite is trans-ferred to the air molecules. Thus, the principle of momentum conservation is not violated.

3. A bolt of mass 0.3 kg falls from the ceiling of an elevator moving down with a uniform speed of 7ms^-1 It hits the floor of the elevator (length of the levator = 3m) and does not rebound. What is the heat produced by the impact? Would your answer be different if the elevator were stationary?

Ans. Potential energy of bolt = mgh.

The bolt does not rebound. Therefore, the whole of the energy is converted into heat energy. Since the value of acceleration due to gravity is the same in all inertial systems, therefore, the answer will not change even if the elevator is stationary.

4. Distinguish between a head-on and an oblique collision.

Ans. If the colliding objects move along the straight line joining their centres, the collision is said to be a head-on collision. If the colliding objects do not move along the straight line joining their centres, the collision is said to be an oblique collision.

5. Throwing mud on the wall is an example of perfectly inelastic collision. Explain.

Ans. A perfect inelastic collision is that in which there is a total loss of kinetic energy of the system. It will happen so, if the two colliding objects stick together and do not move at all. Hence, throwing of mud on the wall is an example of perfectly inelastic collision.

True or False with Reasons:

(i) Work done can be negative.

Ans:  True.

Reason: When the force opposes displacement, such as friction, work done is negative because the force removes energy from the system.

(ii) Power is a vector quantity.

Ans:  False.

Reason: Power is a scalar quantity because it only has magnitude (rate of work done), no direction.

(iii) Kinetic energy can be zero if the object is at rest.

Ans: True.

Reason: Kinetic energy depends on velocity; if velocity is zero, kinetic energy is zero.

(iv) Work is done even if force is perpendicular to displacement.

Ans: False.

Reason: Work done W = Fd cos θ. If θ = 90°, cos 90° = 0 so work done is zero.

(v) Potential energy can be negative depending on the reference point.

Ans: True.

Reason: Potential energy depends on the chosen zero level; it can be set to zero anywhere, so relative potential energy can be negative.

(vi) Elastic collisions conserve both momentum and kinetic energy.

Ans: True.

Reason: By definition, in elastic collisions both momentum and kinetic energy remain constant before and after collision.

(vii) Conservation of mechanical energy applies only if no non-conservative forces act.

Ans: True.

Reason: Friction and other non-conservative forces convert mechanical energy to heat, violating mechanical energy conservation.

(viii) Work done by friction over a closed path is zero.

Ans: False.

Reason: Friction always opposes motion, so work done is negative and accumulates over a closed path, not zero.

(ix) Power is work done divided by time.

Ans: True.

Reason: Power  P = W/t ​ is defined as rate of work done per unit time.

(x) The unit of power ‘horsepower’ equals 746 watts.

Ans: True.

Reason: By definition, 1 horsepower = 746 watts.