# Important Questions Class 11 Physics Chapter 6

## Important Questions for CBSE Class 11 Physics Chapter 6 – Work, Energy and Power

The words “work,” “energy,” and “power” are frequently heard. But in physics, work has a specific and definite meaning. In Chapter 6 of Class 11 Physics, a variety of important concepts are discussed. Students can refer to the set of Class 11 Physics Chapter 6 Important Questions to score high marks on final exams. These solutions can help them learn the most important concepts.

The topics that are covered in this chapter are as follows.

• The work-energy theorem
• Work
• Kinetic energy
• Work done by a variable force
• The work-energy theorem for a variable force
• The concept of potential energy
• The conservation of mechanical energy
• The potential energy of a spring
• Law of conservation of energy
• Power
• Collisions

### CBSE Class 11 Physics Chapter 6 Important Questions – Free Download

Study Important Questions for Class 11 Physics Chapter 6 – Work, Energy and Power

Here, students will find some of the Important Questions for Class 11 Physics Chapter 6. They can additionally access the link provided to review the complete set.

Very Short Answers and Questions- 1 Mark

Q1. Will two bodies which stick together after a collision be elastic or inelastic?

A1. An inelastic collision occurs when two bodies stick together after a collision.

Q2. What happens to an air bubble’s potential energy when it rises in water?

A2. When an air bubble rises in water, its potential energy decreases because work is done by upthrusting on the bubble.

Short Answers and Questions- 2 Marks

Q1. A ball is dropped from height h1 and bounces back to height h2. Determine the value of the restitution coefficient.

A1. As the ball falls from height h1,

The approach velocity will be v1 = √2gh1.

The ball then rebounds to height h2.

As a result, the velocity of separation is v2 = √2gh2.

The restitution coefficient is given by

e = v2v1 = 2gh2√2gh1√

⇒e = h2h1−−√

Q2. When two bodies of different temperatures, T1 and T2 come into thermal contact, they do not always settle to their mean temperature. Why?

A2. Two bodies of different temperatures, T1 and T2, come into thermal contact. Because the thermal capacities of two bodies are not always equal, they do not always settle at their mean temperature.

Q3. List the benefits and drawbacks of a Platinum Resistance thermometer.

A3. The following are the benefits of using a platinum resistance thermometer.

• High measurement precision
• Temperature measurements can be taken over a wide temperature range, from 2600C to 12000C.

The following are the disadvantages of the Platinum Resistance thermometer.

• High Price
• Additional equipment is required, such as a bridge circuit and a power supply.

Long Answers and Questions- 3 Marks

Q1. It is critical to comprehend the sign of work done by a force on a body. Determine whether the following quantities are positive or negative.

(i) A man’s work in lifting a bucket out of a well using a rope tied to the bucket:

Ans: A positive sign of completed work. Force and displacement are both in the same direction in the given case. As a result, the sign of completed work is positive. The work is done on the bucket in this case.

(ii) In the preceding example, work is done by gravitational force:

Ans: The sign of completed work is negative. The directions of force (vertically downward) and displacement (vertically upward) are opposite in the given case. As a result, the sign of completed work is negative.

(iii) Frictional work done on a body sliding down an inclined plane:

Ans: The sign of completed work is negative. Because the frictional force acts in the opposite direction of motion, the work done by the frictional force is negative in this case.

(iv) Work done by an applied force on a body moving with uniform velocity in a rough horizontal plane:

Ans: A positive sign of completed work. The body is moving on a rough horizontal plane in this case. The frictional force is the force that opposes the motion of the body. As a result, a uniform force must be applied to the body in order to maintain a uniform velocity. Because the applied force acts in the direction of the body’s motion, the work done is positive.

(v) The work done by air’s resistive force on a vibrating pendulum to bring it to rest:

Ans: The sign of completed work is negative. The air’s resistive force acts in the opposite direction of the pendulum’s motion. As a result, the work done in this case is negative.

Q2. A 0.5 kg body travels in a straight line with velocity v = ax32, where a = 5m/s2. What is the net force work done during its displacement from x = 0 to x = 2 m?

A2. Ans: In the above question it is given that,

Mass of the body, m= 0.5 kg

Velocity of the body is governed by the equation,

v = ax32 where a = 5m/s2.

Initial velocity, u (at x = 0) = 0

Final velocity v (at x = 2 m) = 102–√m/s

Work done, W = Change in kinetic energy

= 12m(v2−u2)

= 12×0.5×((102–√)2−0)

= 50J

Long Answers and Questions- 4 Marks

Q1. On a frictionless track, a trolley weighing 200 kg moves at a constant speed of 36 km/h. A child of 20 kg runs on the trolley from one end to the other (10 m away) at a speed of 4 relative to the trolley in the opposite direction of its motion and jumps out. What is the trolley’s top speed? How far has the trolley moved since the child began to run?

A1. In the above question, it is given that,

Mass of the trolley, M = 200 kg

Speed of the trolley, v = 36 km/h = 10 m/s

Mass of the boy, m = 20 kg

The initial momentum of the system of the boy and the trolley

= (M+ m)v

= (200+20)×10

= 2200 kg m/s

Let ‘v’ be the final velocity of the trolley with respect to the ground.

The final velocity of the boy with respect to the ground = v′−4

Final momentum = Mv′+m(v′−4)

= 200v′+20v′−80

= 220v′−80

As per the law of conservation of momentum,

Initial momentum = Final momentum

2200 = 220v′−80

⇒v′ = 2280220 = 10.36m/s

Length of the trolley, l = 10 m

Speed of the boy, v′′ = 4 m/s

Time taken by the boy to run, t = 104 = 2.5s.

Thus, the distance moved by the trolley = v′′×t = 10.36×2.5 = 25.9m.

Q1. (a) Define the term potential energy. Give some examples.

Ans. (a) Potential energy is defined as the energy possessed by a body as a result of its position in a field or a change in its configuration, such as a gas compressed in a cylinder, the water wound spring, water raised to an overhead tank in a house, and so on.

(b) Create a graph that depicts the variation of potential energy, kinetic energy, and total energy of a body falling freely on earth from h?

Ans. (b) The graph below depicts the variation of potential energy, kinetic energy, and total energy of a body falling freely on earth from a height h.

(i) The gravitational potential energy decreases as the body falls down until it reaches zero at the earth’s surface.

(ii) Kinetic energy increases as the body fall downward and reaches its peak when the body hits the ground.

(iii) The total mechanical (KE + PE) energy remains constant according to the law of conservation of energy.

Chapter 6 of Class 11 Physics Work, Power and Energy is an important topic for students to cover and achieve high marks in both exams and competitive exams. Students can learn Chapter 6 Work, Power and Energy by practising more and more questions with the help of Important Questions for Class 11 Physics Chapter 6 which is available on the Extramarks platform.

Work Energy And Power Class 11 Important Questions With Answers

The chapter contains interesting topics such as the work-energy theorem, kinetic energy, potential energy, energy conservation, power, collisions, and so on.

Students preparing for exams must be well-versed in the chapter. By practising questions from related topics, students can adapt and approach any type of question they face in the exam. Before beginning to practise Class 11 Physics Work, Energy and Power Important Questions, students should review the chapter.

### Physics Chapter 6 – Work, Energy and Power

Work, energy, and power are crucial chapters in the CBSE Syllabus for Physics in terms of examinations. Students are familiar with the terms “work,” “energy,” and “power” from elementary school. Regular studies and practice are required to master any subject. Work, Energy, and Power is a chapter that can be learned through practice exams. Work, Energy, and Power Class 11 Important Questions covers all of the questions with appropriate examples that students can quickly understand.

Students should understand the entire chapter and remember a few topics in order to answer important questions from Work, Energy, and Power Class 11.

Work is simply the transfer of energy through force.

Work Done: When an external force acts on a body in steady motion, it will experience some displacement; this action is referred to as work done.

Energy is defined as the ability to do work. There are various types of energy, such as electrical energy, solar energy, mechanical energy, and so on. This chapter will primarily cover mechanical energy and its various forms. Mechanical energy is classified into two types:

• Kinetic Energy: The energy gained by an object as a result of its motion is referred to as the object’s kinetic energy.
• Potential Energy: The energy gained by an object as a result of its position is referred to as the object’s potential energy.

Power is the rate at which work is completed.

Work Energy Theorem: The Work-Energy theorem states that the work done on an object by external forces is equal to the change in its kinetic energy.

Law of conservation of energy states that energy can neither be created nor destroyed.

## Why Go For Extramarks?

Extramarks provides a comprehensive set of Important Questions for all subjects and chapters. Our subject matter experts choose questions based on the exam pattern and past years’ questions. These questions provide a thorough understanding of Class 11 Physics Chapter 6 Work, Energy and Power with step-by-step solutions.

### Conclusion

Important Questions for Class 11 Physics Work, Energy and Power are essential for students preparing for exams. Students will gain an understanding of the types of questions in the final examination from the discussion above.  These Important Questions have been curated in a concise manner by subject-matter experts.

Q.1

Read the assertion and reason carefully to mark the correct option out of the options given below.

Assertion: The v-t graph of the particle is shown in the figure. The work is done in the interval AB is positive while in CD is negative.

Reason: Work done on the system is equal to the change in kinetic energy.

Assertion is true but reason is false.

||

Assertion and reason both are false.

||

Both assertion and reason are true and the reason is the correct explanation of the assertion.

||

Both assertion and reason are true but reason is not the correct explanation of the assertion.

Marks:1

Ans

The expression of ?work-energy?theorem is, W?=???K.E. W?=  1 2 m V f 2 ?V i 2 ? Here,? V f ? is the final velocity and V i  is the inital velocity. In segment AB, V f ? is equal to v and V i  is equal to u. So, work done in time  interval 0 to t is, W 0?t ?= 1 2 m v 2 ? 0 2 = 1 2 mv 2 ???(+ve?value)? In segment CD, V f ? is equal to 0 and V i  is equal to v. So, work done in time  interval 3t to 4t, W 3t?4t = 1 2 m 0 2 ? v 2 =? 1 2 mv 2 ????(?ve value)?

Q.2

If the mass and velocity of a body is doubled, then its new kinetic energy is

eight times the original kinetic energy.

||

four times the original kinetic energy.

||

twice the original kinetic energy.

||

half the original kinetic energy.

Marks:1

Ans

eight times the original kinetic energy.

Q.3

The mass of a pendulum bob is 100 g and the length of its string is 1 m. The bob is held such that the string is horizontal and is then allowed to fall. The kinetic energy when the string makes an angle of 30° with the vertical, is

0.849 J

||

1 J

||

2.849 J

||

3.849 J

Marks:1

Ans

0.849 J

Q.4 What happens to the potential energy of a body when conservative force does positive work?

Marks:1

Ans

When conservative forces do positive work, potential energy of a body decreases.

Q.5 Two bodies of masses 5kg and 3kg moving in the same direction along the same straight line with velocities 5m/s and 3m/s respectively suffers one dimensional elastic collision. Find the velocities of two bodies after the collision.

Marks:3

Ans