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## Work, Energy and Power Class 11 MCQs Questions with Answers

Multiple Choice Type Questions

Question 1.

A bullet is fired horizontally and gets embedded in a block kept on a table. If the table is frictionless, then

(a) only momentum is conserved.

(b) only potential energy is conserved.

(c) only K.E. is conserved.

(d) both (a) and (b).

## Answer

Answer: (d) both (a) and (b).

Question 2.

A shell is fired from a canon with a velocity v ms^{-1} at an angle 6 with the horizontal direction. At the highest point in its path, it explodes into two pieces of equal mass. One of the pieces retraces its path to the canon and the speed of the other piece (in ms^{-1}) just after the explosion is

(a) v cos θ

(b) 3v cos θ

(c) 2v cos θ

(d) \(\frac {v}{2}\) cos θ

## Answer

Answer: (b) 3v cos θ

Question 3.

The work performed on an object does not depend upon

(a) the displacement.

(b) the force applied.

(c) the angle at which the force is applied to the displacement

(d) initial velocity of the object.

## Answer

Answer: (d) initial velocity of the object.

Question 4.

A ball is dropped from a height of 15 m. It gets embedded in sand by 10 mm and then stops. Which of the following is conserved?

(a) Temperature

(b) Momentum

(c) Kinetic energy

(d) Both (a) and (c)

## Answer

Answer: (b) Momentum

Question 5.

A chain of length L and mass M is held on a smooth table with its \(\frac {1}{n}\) th part hanging over the edge. The work done in pulling the chain is directly proportional to

(a) n^{-3}

(b) √n

(c) n

(d) n^{-2}

## Answer

Answer: (d) n^{-2}

Question 6.

A pump delivers water at the rate of V cubic meter per second. By what factor its power should be raised so that it delivers water at the rate of nV cubic metre per second.

(a) n³

(b) √n

(c) n

(d) n²

## Answer

Answer: (a) n³

Question 7.

Liquid of density ρ flows along a horizontal pipe of uniform area of cross-section ‘a’ with a velocity v through a right angled bend. What force should be applied to the bend to hold it in equilibrium?

(a) \(\frac {av^2ρ}{2}\)

(b) \(\frac {av^2ρ}{√2}\)

(c) 2av²ρ

(d) √2 av²ρ

## Answer

Answer: (c) 2av²ρ

Question 8.

A body of mass M accelerates uniformly from rest to a velocity v in time t. What is the instantaneous power delivered to the body at time T.

(a) \(\frac {mv}{t}\)T

(b) \(\frac {mv^2}{t}\)T

(c) \(\frac {m^2v^2}{t^2}\)T

(d) \(\frac {mv^2}{t^2}\)T

## Answer

Answer: (d) \(\frac {mv^2}{t^2}\)T

Question 9.

A man weighing 50 kgf carries a load of 10 kgf to the top of the building in 5 minutes. The work done by him is 10^{5} J. If he carries the same load in 10 minutes, the work done by him will be:

(a) 10^{5} J

(b) 5 × 10^{5} J

(c) 12 × 10^{5} J

(d) 2.5 × 10^{5} J

## Answer

Answer: (a) 10^{5} J

Question 10.

If v be the instantaneous velocity of a body dropped from the top of a tower, when it is located at a height h, then which of the following remains constant?

(a) gh + \(\frac {1}{2}\) v²

(b) gh – \(\frac {1}{2}\) v²

(c) gh + v²

(d) gh – v²

## Answer

Answer: (a) gh + \(\frac {1}{2}\) v²

Question 11.

A ball B_{1}of mass m is moving with a velocity v along north. It collides with another ball B_{2} of same mass moving with a velocity v along east. After the collision, both the balls stick together and move along north east. The velocity of the combination is

(a) \(\frac {v}{√2}\)

(b) √2v

(c) 2v

(d) v

## Answer

Answer: (a) \(\frac {v}{√2}\)

Question 12.

A ball B_{1} of mass m moving with velocity u, collides head on with another ball B_{2} of the same mass at rest. Given that the coefficient of restitution is e. Then the ratio of velocities of two balls after collision will be

(a) \(\frac {1+e}{1-e}\)

(b) e

(c) \(\frac {1+e}{2}\)

(d) \(\frac {1-e}{2}\)

## Answer

Answer: (a) \(\frac {1+e}{1-e}\)

Question 13.

A vehicle of mass m is moving on a rough horizontal road with a momentum p. If the coefficient of friction between the tyres and the road be µ, then the stopping distance is given by

(a) \(\frac {p}{2µm^2g}\)

(b) \(\frac {p}{2µmg}\)

(c) \(\frac {p^2}{2µmg}\)

(d) \(\frac {p^2}{2µm^2g}\)

## Answer

Answer: (d) \(\frac {p^2}{2µm^2g}\)

Question 14.

A uniform chain of length l and mass m is lying on a smooth table and one-third of its length is hanging vertically down over the edge of the table. If g be the acceleration due to gravity, then the work required to pull the hanging part on the table is :

(a) \(\frac {mg l}{3}\)

(b) \(\frac {mgl}{9}\)

(c) \(\frac {mgl}{18}\)

(d) mg l

## Answer

Answer: (c) \(\frac {mgl}{18}\)

Question 15.

A ball of mass m is dropped from a height h on a platform fixed at the top of a vertical spring and it is depressed by a distance x. What is the spring constant?

(a) \(\frac {2mg}{x}\)

(b) \(\frac {2mgh}{x^2}\)

(c) \(\frac {2mg(h+x)}{h^2}\)

(d) \(\frac {2mg(h+x)}{x^2}\)

## Answer

Answer: (d) \(\frac {2mg(h+x)}{x^2}\)

Question 16.

The slope of the potential energy versus position vector gives

(a) momentum

(b) force

(c) work done

(d) power

## Answer

Answer: (b) force

Question 17.

The slope of the kinetic energy versus position vector gives the time rate of change of:

(a) momentum

(b) force

(c) work done

(d) power

## Answer

Answer: (a) momentum

Question 18.

A bus weighing 100 quintals moves on a rough road with a constant speed of 72 kmh^{-1}. The friction of the road is 9% of its weight and that of air is 1 % of its weight. What is the power of the engine? Take g = 10 ms^{-2}.

(a) 100 kW

(b) 150 kW

(c) 200 kW

(d) 50 kW

## Answer

Answer: (c) 200 kW

Question 19.

A metre rod is pivoted at its end and stands vertically. If it is displaced through 60° with the vertical, what will be the ratio of its potential energy in this position to its maximum potential energy?

(a) 0.25

(b) 0.75

(c) 0.80

(d) 0.50

## Answer

Answer: (d) 0.50

Question 20.

A bullet is fired into a block of sand and its velocity decreases by 50% when it penetrates through 9 cm. What will be the total distance penetrated by the bullet?

(a) 9 cm

(b) 10 cm

(c) 12 cm

(d) 18 cm

## Answer

Answer: (c) 12 cm

Fill in the blanks

Question 1.

When a body is dropped from a certain height on the ground, the work is done on the body ……………. and is ……………….

## Answer

Answer: by the force of gravity, positive

Question 2.

When it is lifted from the ground to a certain height, the work is done on the body ……………. and is ……………

## Answer

Answer: against the force of gravity, negative

Question 3.

The statement that inertial mass of a body is equal to the gravitational mass is called ……………

## Answer

Answer: principle of equivalence

Question 4.

When a vertical force equal to the weight of a body is applied to it, then its acceleration is ……………..

## Answer

Answer: zero.

Question 5.

When work done is zero, then the speed of a body is ……………..

## Answer

Answer: uniform

Question 6.

Coefficient of restitution is one for ……………… collision.

## Answer

Answer: perfectly elastic collision

Question 7.

The coefficient of restitution is zero (e = 0) for ……………… collision which means that ……………….. of the colliding body is lost and is changed to other forms like ………………. or …………………..

## Answer

Answer: perfectly inelastic, kinetic energy, sound energy, or heat energy

Question 8.

The mass of a body increases with the increase in the velocity of the particle according to the relation ………………..

## Answer

Answer: m = \(\frac {m_0}{\sqrt{1-\frac{v^2}{c^2}}}\)

Question 9.

Mass of the particle becomes infinite if it moves with the ……………….. and the acceleration produced in the body by a given force F becomes ………………

## Answer

Answer: velocity of light c = 3 × 10^{8} ms^{-1}, zero (∵ a = \(\frac {F}{m}\) = \(\frac {F}{∞}\) = 0)

Question 10.

E = mc² shows that mass and energy are …………….

## Answer

Answer: inter convertible

Energy is transferred from one form to another.

Name the transformations of energy in the following in the form ……………….. to ………………..

Question 11.

lifting of a book by a boy ………………..

## Answer

Answer: Lifting of a book by a boy transforms energy from chemical to gravitational.

Question 12.

burning of candle ………………..

## Answer

Answer: Burning of candle transforms energy from chemical to light and heat.

Question 13.

a moving truck on a road ………………..

## Answer

Answer: A moving truck on a road transforms energy from chemical to kinetic energy of motion.

Question 14.

emission of light by Sun ………………..

## Answer

Answer: Emission of light by Sun transforms energy from nuclear to electromagnetic energy.

Question 15.

The work done against friction is ……………….. proportional to the force with which the surfaces are pressed together.

## Answer

Answer: directly

Question 16.

If the momentum of a body is doubled then its K.E. becomes ………………..

## Answer

Answer: four times

Question 17.

The sum of K.E. and P.E. for an isolated system is always ………………..

## Answer

Answer: constant

Question 18.

If the range of a projectile be R, then its K.E. is minimum when horizontal distance covered by it is ………………..

## Answer

Answer: \(\frac {R}{2}\)

Question 19.

………………. is not conserved during an inelastic collision.

## Answer

Answer: K.E.

Question 20.

When a bullet striking a block gets embedded in it, then the nature of collision is ……………….

## Answer

Answer: perfectly inelastic

Question 21.

………………. is a non-conservative force.

## Answer

Answer: friction

Question 22.

For a perfectly inelastic collision, the coefficient of restitution is ……………….

## Answer

Answer: zero

Question 23.

The work done …………….. updn the time taken in doing it.

## Answer

Answer: does not depend

Question 24.

The work done by the conservative force 1s always ……………..

## Answer

Answer: positive

Question 25.

The P.E. gained by the body raised from the surface of Earth by a height equal to radius of Earth is ……………..

## Answer

Answer: mg \(\frac {R}{2}\)

Question 26.

K.E. of a projectile is …………….. at the highest point of its trajectory.

## Answer

Answer: minimum

Question 27.

The work done on a body by a resultant external force is always ………………. to the change in its K.E.

## Answer

Answer: equal

Question 28.

A body is suspended by vertical string. The work done on the body by the tension in the string is …………….

## Answer

Answer: zero

Question 29.

Power is ………………. of force and velocity.

## Answer

Answer: scalar product

Question 30.

Work is ………………. of force and displacement.

## Answer

Answer: scalar product

Question 31.

1 kwh is the energy consumed by an appliance of power I kw in ………….

## Answer

Answer: 1 hour

Question 32.

The work done by a conservative force moving an object on a closed path is …………….

## Answer

Answer: zero.

Question 33.

In a perfectly inelastic collision, the two bodies ………………… after collision.

## Answer

Answer: stick together

Question 34.

For an inelastic collision, the coefficient of restitution lies between ………………

## Answer

Answer: 0

Question 35.

Kinetic energy increases during a ……………….

## Answer

Answer: super elastic collision

Question 36.

………………. energy results from the chemical bounding between the atoms.

## Answer

Answer: Chemical

Question 37.

………………. energy results due to the separation between two objects in the gravitational field.

## Answer

Answer: Gravitational

Question 38.

………………… energy between two nucleons is due to nuclear force.

## Answer

Answer: Nuclear

Question 39.

Chemical, gravitational and nuclear energies are the ……………….. for different types of forces in nature.

## Answer

Answer: Potential energies

True/False Type Questions

1. Which of the following statement is True/False?

(a) Work done can be positive, negative and zero.

(b) A teacher sitting in a chair is dong work.

(c) Work is the cross product of force and displacement.

(d) Work done by a coolie in carrying a bag on his head is zero.

## Answer

Answer:

(a) True

(b) False

(c) False

(d) True

2. Which of the following statement is True/False?

(a) The principle of conservation of linear momentum can be strictly applied during a collision between two particles provided the time of impact is extremely small.

(b) In an inelastic collision, the linear momentum is conserved but not the kinetic energy.

(c) The collision is said to be elastic if two bodies stick together after collision.

(d) The unit of energy is increased by 16 times if the unit of force and length be each increased by 4 times.

## Answer

Answer:

(a) True

(b) True

(c) False

(d) True

3. Tell which of the following statement is True/False?

(a) Momentum is conserved in elastic collision but not in inelastic collision.

(b) Total kinetic energy is conserved in elastic collision but momentum is not conserved in elastic collision.

(c) Both K.E. and momentum are conserved in all types of collision.

(d) Total energy, K.E. and the momentum is conserved in elastic collision.

## Answer

Answer:

(a) False

(b) False

(c) False

(d) True

4. Which of the following statement is True/False?

(a) Both momentum and energy are conserved in an inelastic collision.

(b) Neither momentum nor energy is conserved in an inelastic collision.

(c) Momentum is conserved but not the K.E. in an inelastic collision.

(d) Momentum is not conserved but the K.E. is conserved in an inelastic collision.

## Answer

Answer:

(a) False

(b) False

(c) True

(d) False

5. Which of the following statement is True/False?

There will be an increase in potential energy of the system if work is done upon the system by

(a) a conservative force.

(b) a non-conservative force.

(c) any conservative or non-conservative force.

## Answer

Answer:

(a) True

(b) False

(c) False

6.

Which of the following statement is True/False?

(a) The gain in the P.E. of an object of mass m raised from the surface of earth to a height equal to the radius R is \(\frac {mgR}{2}\).

(b) 1 eV = 1.6 × 10^{-19} J

(c) Power is the cross-product of force and velocity.

(d) Work is the dot product of force and displacement.

## Answer

Answer:

(a) True

(b) True

(c) False

(d) True

7. Which of the following statement is True/False?

(a) A teacher rubbing the blockboard by a duster is doing no work.

(b) A light and a heavy body have equal K.E. of translation. The heavier body has larger momentum.

(c) A bullet is fired from a rifle. If the rifle recoils freely, then the K.E. of the rifle is greater than that of the bullet.

(d) The energy produced when 10 gram of coal is burnt is 9 × 10^{4} J.

## Answer

Answer:

(a) True

(b) True

(c) False

(d) True

8. Tell which one of the following statement is True/False?

(a) A truck and car having same K.E. cover equal distances before stopping after applying equal retarding force through brakes.

(b) 1 kg m = 9.8 J

(c) 1 J = 10^{7} erg

(d) For an elastic collision, the velocity of separation after collision is always equal to the velocity of approach before collision.

## Answer

Answer:

(a) True

(b) True

(c) True

(d) True

9. Tell which of the following statement is True/False?

(a) Friction is non-conservative force.

(b) Gravity is a conservative force.

(c) No work is done against gravity while moving an object along horizontal.

(d) Kilowatt-hour is the unit of energy.

## Answer

Answer:

(a) True

(b) True

(c) True

(d) True

10. Tell which of the following statements are True/False?

(a) The forces involved during the elastic collision are conservative in nature.

(b) K.E. lost in an inelastic collision appears in some other form of energy such as heat, sound etc.

(c) Mechanical energy is not converted into any other form of energy in an elastic collision.

(d) Coefficient of restitution is zero (e = 0) for a perfectly inelastic collosion.

## Answer

Answer:

(a) True

(b) True

(c) True

(d) True

Match Type Questions

Column I | Column II |

(a) Conservative force | (i) work |

(b) Non-conservative force | (ii) power |

(c) Dot product of F and v | (iii) gravity |

(d) Dot product of F and s | (iv) force of friction |

## Answer

Answer:

Column I | Column II |

(a) Conservative force | (iii) gravity |

(b) Non-conservative force | (iv) force of friction |

(c) Dot product of F and v | (ii) power |

(d) Dot product of F and s | (i) work |

Column I | Column II |

(a) Work done is zero | (i) by gravity |

(b) Work done is positive | (ii) electrostatic force |

(c) Work done is negative | (iii) against gravity |

(d) is a conservative force | (iv) by centripetal force |

## Answer

Answer:

Column I | Column II |

(a) Work done is zero | (iv) by centripetal force |

(b) Work done is positive | (i) by gravity |

(c) Work done is negative | (iii) against gravity |

(d) is a conservative force | (ii) electrostatic force |

Column I | Column II |

(a) Absolute S.I. unit of work | (i) erg |

(b) Gravitational S.I. unit of work | (ii) gram cm |

(c) Gravitational C.G.S. unit of work | (iii) kg m |

(d) Absolute C.G.S. unit of work | (iv) Joule |

## Answer

Answer:

Column I | Column II |

(a) Absolute S.I. unit of work | (iv) Joule |

(b) Gravitational S.I. unit of work | (iii) kg m |

(c) Gravitational C.G.S. unit of work | (ii) gram cm |

(d) Absolute C.G.S. unit of work | (i) erg |

Column I | Column II |

(a) S.I. unit of power | (i) Electron volt (eV) |

(b) Unit of energy | (ii) 9.8 J |

(c) 1 horse power | (iii) Watt |

(d) 1 kgm | (iv) 746 W |

## Answer

Answer:

Column I | Column II |

(a) S.I. unit of power | (iii) Watt |

(b) Unit of energy | (i) Electron volt (eV) |

(c) 1 horse power | (iv) 746 W |

(d) 1 kgm | (ii) 9.8 J |

Column I | Column II |

(a) 1 kg m | (i) 1 Js^{-1} |

(b) 1 gm cm | (ii) 1 kg f × 1 m |

(c) 1 Watt | (iii) C.G.S. absolute unit of power |

(d) 1 erg s^{-1} |
(iv) 1 g f × 1 cm |

## Answer

Answer:

Column I | Column II |

(a) 1 kg m | (ii) 1 kg f × 1 m |

(b) 1 gm cm | (iv) 1 g f × 1 cm |

(c) 1 Watt | (i) 1 Js^{-1} |

(d) 1 erg s^{-1} |
(iii) C.G.S. absolute unit of power |

Column I | Column II |

(a) S.I. gravitational unit of power | (i) [ML²T^{-3}] |

(b) C.G.S. gravitational unit of power | (ii) [ML²T^{-2}] |

(c) Dimensional formula of energy | (iii) Kg f ms^{-1} |

(d) Dimensional formula of power | (iv) g f cms^{-1} |

## Answer

Answer:

Column I | Column II |

(a) S.I. gravitational unit of power | (iii) Kg f ms^{-1} |

(b) C.G.S. gravitational unit of power | (iv) g f cms^{-1} |

(c) Dimensional formula of energy | (ii) [ML²T^{-2}] |

(d) Dimensional formula of power | (i) [ML²T^{-3}] |

Column I | Column II |

(a) Momentum and total energy are conserved and K.E. is not conserved | (i) elastic collision |

(b) Momentum, K.E. and total energy are conserved | (ii) inelastic collision |

(c) Inelastic collision | (iii) force involved are conservative in nature |

(d) Elastic collision | (iv) forces involved are non-conservative in nature |

## Answer

Answer:

Column I | Column II |

(a) Momentum and total energy are conserved and K.E. is not conserved | (ii) inelastic collision |

(b) Momentum, K.E. and total energy are conserved | (i) elastic collision |

(c) Inelastic collision | (iv) forces involved are non-conservative in nature |

(d) Elastic collision | (iii) force involved are conservative in nature |

Column I | Column II |

(a) Bodies move along the same straight line before and after collision | (i) they are of equal masses |

(b) Bodids exchange their velocities after collision in one dimension if | (ii) B starts moving with the velocity of A |

(c) When a body A collides with B of equal mass at rest, then body A comes to rest and | (iii) A starts moving with equal velocity in opposite direction and B remains at rest i.e. A rebounces |

(d) When a light body A collides with a heavy body B at rest, then | (iv) head-on or one dimensional collision |

## Answer

Answer:

Column I | Column II |

(a) Bodies move along the same straight line before and after collision | (iv) head-on or one dimensional collision |

(b) Bodids exchange their velocities after collision in one dimension if | (i) they are of equal masses |

(c) When a body A collides with B of equal mass at rest, then body A comes to rest and | (ii) B starts moving with the velocity of A |

(d) When a light body A collides with a heavy body B at rest, then | (iii) A starts moving with equal velocity in opposite direction and B remains at rest i.e. A rebounces |

Column I | Column II |

(a) When a conservative force does positive work on a body, then it is displaced in the direction of force and it approaches the s centre of force, so | (i) decrease in K.E. |

(b) Work done by a body its P.E. decreases against friction causes | (ii) its P.E. decreases |

(c) The rate of change of total momentum of many particle system | (iii) is directly proportional to the external force |

## Answer

Answer:

Column I | Column II |

(a) When a conservative force does positive work on a body, then it is displaced in the direction of force and it approaches the s centre of force, so | (ii) its P.E. decreases |

(b) Work done by a body against friction causes | (i) decrease in K.E. |

(c) The rate of change of total momentum of many particle system | (iii) is directly proportional to the external force |

Column I | Column II |

(a) Two colliding bodies get stick together after collision | (i) for perfectly elastic collision |

(b) e is equal to 1 | (ii) for perfectly inelastic collision |

(c) Velocity of approach > velocity of separation | (iii) for inelastic collision |

## Answer

Answer:

Column I | Column II |

(a) Two colliding bodies get stick together after collision | (ii) for perfectly inelastic collision |

(b) e is equal to 1 | (i) for perfectly elastic collision |

(c) Velocity of approach > velocity of separation | (iii) for inelastic collision |

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