A running man has the same kinetic energy as that of a boy of hal

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 Multiple Choice QuestionsMultiple Choice Questions

41.

A spring gun of spring constant 90 N/cm is compressed 12 cm by a ball of mass 16 g. If the trigger is pulled, the velocity of the ball is

  • 50 ms-1

  • 9 ms-1

  • 90 ms-1

  • 60 ms-1


42.

A particle is moving under the influence of a force given by F = kx, where k is a constant and x is the distance moved. The energy (in joules) gained by the particle in moving from x = 0 to x = 3 is

  • 2 k

  • 3.5 k

  • 4.5 k

  • 9 k


43.

The work done in moving an alpha particle between two points having potential difference 25 V is

  • 8 × 10-18 J

  • 8 × 10-19 J

  • 8 × 10-20 J

  • 8 × 10-16 J


44.

A rod AB of mass 10 kg and length 4 m rests on a horizontal floor with end A fixed so as to rotate it in vertical plane about perpendicular axis passing through A. If the work done on the rod is 100 J, the height to which the end B be raised vertically above the floor is

  • 1.5 m

  • 2.0 m

  • 1.0 m

  • 2.5 m


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45.

A particle is released from a height S. At certain height its kinetic energy is three times its potential energy. The height and speed of the particle at that instant are respectively

  • S4, 3gS2

  • S4, 3gS2

  • S2, 3gS2

  • S4, 3gS2


46.

An electric pump is used to fill an overhead tank of capacity 9 m3 kept at a height of 10 m above the ground. If the pump takes 5 min to fill the tank by consuming 10 kW power, the efficiency of the pump should be (Take g = 10 ms-2)

  • 60 %

  • 40 %

  • 20 %

  • 30 %


47.

Potential energy in a spring when stretched by 2 cm is U. Its potential energy, when stretched by 10 cm is

  • U25

  • U5

  • 25 U

  • 5 U


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48.

A running man has the same kinetic energy as that of a boy of half his mass. The man speeds up by 2 ms-1 and the boy changes his speed by x ms-1, so that the kinetic energies of the boy and the man are again equal. Then x in ms-1 is

  • - 22

  • + 22

  • 2

  • 2


B.

+ 22

Let vM is velocity of man, vB of boy, then kinetic energy

K = 12 Mv2M = 12 . M2 . vB2     v2M = vB22                                .......... (i) 2vM = vB

When man speeds up 2 ms-1 and boy changes his speed by x ms-1. Then,

12 M vM + 22 = 12 . M2 . vB + x2    vM + 22 =  vB + x22                         .......... (2)

From Eq. (1), we have

2vM + 22 = 2vM + x2 2vM + 2 = 2vM + x         + 22 = x


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49.

Two cars A and B are travelling in the same direction with velocities v1 and v(v1 > v2). When the car A is at a distance d behind the car B, the driver of the car A applies the brake producing uniform retardation, a. There will be no collision when

  • d < v1 - v22a

  • d > v12 - v222a

  • d > v1 - v222a

  • d < v12 - v222a


50.

The momentum of a body is increased by 25%. The kinetic energy is increased by about 

  • 25 %

  • 5 %

  • 56 %

  • 38 %


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