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UNIQUE LEARNING CENTRE, ULLOOR, TVPM www.uniquetvm.com Physics Work ,Power & Energy Std: XI Marks: 200,Time: 1 hour 1. Work done by a force �� producing a displacement �� is given by:

A) W = �� + �� B) W = �� - �� C) W = ��. �� D) W = �� � �� E) W= F � ��

2. A particles moves under a force F = cx from x = 0 to x =�� .The work done in this process is A) ���� B)���� /2 C) ���� D) (1 /2) ���� E) zero

3. The initial and final position vectors of a particle under a force����� = 3i + 4j Newton are given by ��� = �� + 2�� metre and ��� = 4�� + 6�� metre. Then the work done in joule is A) 12.5 B) 10 C) 5 D) 25 E) 30

4. A particle moves along a circular path under the action of a force. The work done by the force is: A) zero B) positive C) negative D) variable work E) depends on the nature of the force

5. Air expands from 50 litres to 150 litres at a constant pressure of 10� Newton / �� . The work done is: A)10�joule B) 10� joule C)10�joule D) 10� joule E) 10� joule

6. A chord is used to lower vertically a block of mass m, through a distance d at a constant acceleration g/4 .The work done by the chord is: A) mgd B) mgd /2 C ) -3mgd /4 D) mgd/4 E) –mgd /2

7.One person takes 10s to raise a load from floor to the top of a building. Another person takes 5 s .Work done: A) by the first is more B) by the first is less C) is same in both D) become 1/ 5 in the first case E) become 5 times in the first case

8. A body of mass 10 kg is dropped to the ground from height of 10 metres. The work done by the gravitational force is: A) -490 joule B) 490 joule C) -980 joule D) 980 joule E) zero

9. A man pushes a wall and fails to displace it .He does: A) negative work B) positive work C) maximum positive work D) maximum negative work E) no work at all

10. The unit of work in C.G.S. system is erg. 1 kilo joule A)10� erg B) 10� erg C) 10�� erg D) 10�� erg E)10� erg

11. A rod of mass m and length l lying on a horizontal table. The work done in making it stand on one end will be: A) mgl B) mgl/2 C) mgl / 4 D) 2mgl E) mgl/3 12. Given W = �� . �� = 0 and � � 0 , � � 0 then

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A)�� � �� B) �� � �� C) ����� �� �� D) �� � �� /2 E) angle between �� and �� is 45� 13. A man of mass 60kg climbs a 20m long incline to the top of a building 10 m high, what is the work done by him? A) 12kj B) 6kj C) 3kj D) 1.5 kj E) 0.5kj

14. The work done by an external force equals the change in: A) kinetic energy only B) potential energy only C) heat energy only D) chemical energy only E) total energy

15) How many times should the power developed by the engine of a ship increase to double its velocity if the resistance of the water to the motion of the ship increases in proportion to the square of the velocity: A) 2times B) 4times C) 8times D) 16 times E) 32 times

16. A bullet of mass a and velocity b fired into a large block of mass c. The final velocity of the system is:

A) ����

.b B) ����

.b C) ����

.a D) ����

.b E) �����

17. A ball is allowed to fall from a height of 10m. If there is 40% loss of energy due to impact, then after one impact the ball will go upto: A) 16 m B) 8m C) 4m D) 6m E) 2m

18. A bomb of 12 kg explodes into two pieces of masses 4kg and 8kg .The velocity of 8kg mass is 6m/sec. The K.E of the other mass is: A)48joule B) 32 joule C) 24 joule D)288 joule E) 144joule

19.K is the force constant of a spring. The work done in increasing its extension from �� to �� is: A) K (�� - ��) B) K (�� + ��) C) K (��� + ��� ) D) K (��� - ��� ) E) (K/2) (��� - ��� )

20. A child is swinging in a swing. He is one metre above the ground at the lowest point and 2 metre above the ground at the highest point. The speed of the child at the lowest point is (g = 10m/s2 ) A) 10m��� B) 7.8m��� C) 6.4 m��� D) 4.5m��� E) 12m���

21. A bullet of mass �� moving with a velocity u strikes wooden block of mass �� suspended from a string and get embedded in it. The block then rise to a high H. The value of u is: A) �����

�� �2�� B) ��

����� �2�� C) �����

����� �2��

D)� �������

��2gH E) �2��

22.A body falls from a large height. The ratio of the K.E attained by it at the end of three seconds after the beginning of motion to the increment in K.E during the next three seconds is: A) 1:1 B) 1:2 C) 1:5 D) 1:4 E) 1:3

23. In which cases does the PE decrease? A) On compressing a spring B) on stretching a spring C) rising of an air bubble in water

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D) for a body falling freely E) both C & D 24. A truck and a car are moving with the same KE are stopped by applying same retarding force by means of brakes. Which one will stop at a smaller distance: A)truck B) car C)both will stop at a same distance D)depends on friction E) cannot be predicted

25.A body of mass 3kg is dropped from the top of a tower of height 75 m then its KE after 3 seconds will be: A) 1296 J B) 1048 J C) 746 J D) 557J E)120J

26. The electron is accelerated through a P.D of 10 V. The additional energy acquired by the electron is: A) 1.6� 10���J B) 1.6� 10���J C) 1.6� 10��� eV D) 1.6 � 10���eV E) 1.6� 10���J

27. A light spring of force constant 8 N/m is cut into two equal halves and two are connected in parallel. The equivalent force constant of the system in N/m is: A) 16 B) 32 C) 8 D) 24 E) 64

28. The units of force and length are made three times their earlier values. Initial energy of a system was 81 joule. What will be the energy of the same system in new units? A) 243 B) 81 C) 9 D) 729 E) 3

29. A metre scale of mass 100g is pivoted at one end .If it is held 30�with the horizontal. What is the �. �.associated with it: A) 0.1� B) 0.15� C) 0.2� D) 0.25� E) 0.5�

30. A work of 25� is done on a body of mass 2kg to set in motion. If it is used to increases the KE of the body, the velocity attained by it in ���� is: A) 5 B) 12.5 C) 25 D) 50 E) 75

31. If the speed of vehicle increases by 2 m/s , its K.E is doubled. What was the original speed of the vehicle? A) (√2� 1)m/s B) √2m/s C) 2(√2 � 1)m/s D)√2 (√2 � 1)m/s E) 2m/s

32. A constant force is applied to a body. The power generated is related to time elapsed (t) as:

A)P α �� B) P α t C) P α √� D) P α ��� E) P α ��

33. An electric motor creates a tension of 4500 N in a cable and reels it at the rate of 2 m/sec. What is the power of the motor? A) 15kW B) 9kW C) 225 W D) 250 W E) 9000HP

34. A motor of 100 HP moves with uniform speed of 72 km/hr. The forward thrust applied by the engine on the car is: A) 3730 N B) 3550N C) 3839N D) 3333N E) 3000N 35. A lead ball of mass 2kg moving with 1.5m/s hits against a ball of mass 3kg at rest. If the second ball moves with 1m/s after the impact in the original direction of the first ball, the loss in KE due to impact is: A)0.033J B)0.75J C) 1.5J D)2.25J E)5J

36. A block of mass m moving with a speed �collides with another block of mass 2 m at rest. If the lighter block comes to rest after collision, what is the coefficient of restitution: A) ½ B) 1/3 C) ¼ D)1/5 E) 1/6

37. A car of mass m is driven with an acceleration a along a straight level road against constant resistance R when the velocity is the power of the engine is: A) R � V B) m� a � V C) (R+ma)V D) (R – ma)V

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38. A moving car encounters air resistance which is proportional to the square of the speed of the car . The ratio of the power required at 40 km/hr to that required at 80 km/hr ,is A) 1:6 B) 1: 8 C) 1:6 D)16:1 E)32:1

39. A car of mass has an engine which can deliver power P. The minimum time in which the car be accelerated from rest to a speed v is: A) P/��� B) P��� C) 2 P���

D) ���

� E) ���

��

40.A nucleus ruptures into two nuclear parts, which have their velocity ratio equal to 2:1 What will be the ratio of their nuclear size (nuclear radius)

A) 2�� :1 B) 1 :2

�� C) 3

�� : 1 D)1:1

41. A solid sphere is moving and it makes an elastic collision with stationary sphere of half its radius. After collision it comes to rest the ratio of the densities of the material of the second to that of the first is: [A] 2 [B] 4 [C] 8 [D]16 [E] 36

42. A ball of mass 50 g is thrown upwards. It rises to a height of 100m. At what height its KE will be reduced to 70%: [A] 30 m [B] 40 m [C] 60m [D] 70m [E] 80m

43. A body projected up with velocity��. Another body is projected at 45�. Both reaches the same height. What is the ratio of their initial kinetic energies? [A] 1/4 [B] 1/3 [C] 1/2 [D]1 [E] 1/8

44. A ball of mass m moving with a constant velocity strikes against a ball of same mass at rest. What will be the ratio of the velocities after collision (e- coefficient of restitution) [A] ���

��� [B] ���

��� [C] ���

��� [D] ���

��� [E] �

���

45. Two identical balls A and B moving with 5m/s and -3m/s respectively collide head on elastically. Their velocities after collision in m/s: [A] 5,3 [B] -3 , 5 [C] -3, -5 [D] 3,5 [E] 0, 3

46. Two balls at same temperature is collide. What is conserved: [A] Temperature [b] Velocity [C] K.E [D] Momentum [E] None

47. A block of mass 2kg slides down a curved track that is one quarter of a circle of radius 1 m. Its speed at the bottom is 4m/s. Work done by the frictional force is (g=10m/s)

[A]+4J [ B]8J [C]25J [D]-8J [E]20J

48. A stone is falling freely in free space. Its velocity is x when it has lost y units of P.E in the gravitational field of earth. Then the mass of the stone is: [A]xy [B]��

�� [C]x+y [D]��

� [E]��

�+9.8

49. A weight suspended from the free end of a spring produces an extension of 3 cm. The spring is cut into two parts so that the length of the longer part is 2/3 of its length. If the same weight is suspended from the longer part of spring , the extension produced will be: [A] 0.1 cm [B] 0.5cm [C]1cm [D] 10cm [E] 2cm

50. If a shell fired from a cannon explodes in mid air , its total : [A] Momentum increases [B] Momentum decreases [C] K.E increases [D] K.E decreases [E] K.E. remains constant

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Answer key and explanation

1. C

W = � cxdx��� = ���

�

���

�� = �

� �x��

2. B

W = ��. x�� x�� = ������ - ������ X = �� - �� = ( 4i + 6j) – (i + 2j) = ( 3i + 4j) F.X = ( 3i + 4j) ( 3i + 4j) = 9 + 16= 25

3. D

4. A Work done by the centripetal force is always zero

5. C W = P � ∆� = 10�(150-50)10�

6. C

W = -F.d = -m�� � ���d = - 3mg �

�

7. C

Work depends only on height and force

8. D W = m� � �h = 10�9.8� 10 = 980J

9. E

10. C 1 Joule = 10�erg , 1K joule = 10��erg

11. B

W = m� � � �� (height from the centre of mass )

12. A Work is zero when F is perpendicular to�

13. B W = m� � �h

14. E

15. C � ∝ �� p = F.v ∴ p ∝�� v → 2v p →8p

16. B

a� � = (a +c) v v = ������

17. D ���������

��� = m� � �h h = 6m

18. D 12� 0 = 4 � v + 8 � 6

v = ���

= 12 K.E = �� � 4 � 144 = 288J

19. E

W = �� K ���� � ����

20. D �� ��� = �2�– mg � 1

= mg � 1 v = �2� = 4.5 ����

21. A ��xu = (�� +�� ) v ∴ v = ����

�����

�� � (�� +�� )�� = (�� +�� )gH

�� � � ���

������� = gH �� = ������

���� 2gH

u = �������

��2��

22. E 23. E

24. C Both truck and car have the same K.E . and same retarding force is applied . Work = change in KE. F.x = (1/2)���

25. A V = 10 � 3 = 30m/s ;

K.E . ����� = �

� �3 �900 = 1296J

26. B Energy = e �V = 1.6 � 10��� �10 = 1.6 � 10���

27. B K = �� � �� = 32 [��= 2� 8, �� = 2� 8J

28. D Unit changes to 9 times so measured value change to (1/9)th

29. D x

30o

Sin 30 = ��/�

x = ��

PE = m� � �x = 0.1 �10 �(1/4) = 0.25J

30. A

Work = ��� � �� = 25 v = ������

� = 5m/s

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31. C

32 B P = F.V= m� � � �� P ∝ ��

33. B P = F.v = 4500 �2 = 9000 W

34. A

F = ��

= �������������

= ��������������

= 3730 N

35. B 2 � 1.5 + 3 � 0 = 3 �1 = 2 �v v = 0

loss in KE = ��� 2 � �1.5�� - �

�� 3 � 1� = 2.25 – 1.5 = 0.75 J

36. A

37. C

38. B P = F.V F ∝ �� ∴ P ∝ ��

39. E

40. B

41. C Since collision is elastic, �� = ��

����� � ��� - �

� � ��

������

����

= ��/���

�� = �

� ��

�� = 8

42. A ����������

��� = m� � �h h = 30m

43. C

44. A �� = 0 �� = �� ���� + �� �� = ���� + �� �� �� = ��+ �� e = �����

�� = �����

����� � by ��

�1 ������ = e �1 ���

���

e + ������

- 1 + ����

= 0 ����

= ������

45. B If the masses are equal and collision is elastic they will exchange their velocities

46. D

47. A

48. B

�� m �x� = y

49. E

K’ = �� K mg = k.3 mg = k’ . x’

mg = �� k’ . x’ �

� kx’ = k.3 x’ = 2

50. C

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