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Work, Energy and Power · Question 57

AIPMT 2003MCQMedium📈 Topic in 12% papers+4−1
1

A stone is tied to a string of length l and is whirled in a vertical circle with the other end of the string as the centre. At a certain instant of time, the stone is at its lowest position and has a speed u. The magnitude of the change in velocity as it reaches a position where the string is horizontal (g being acceleration due to gravity) is

  1. 2(u2 - gl)
  2. u2 - gl
  3. u - u2 - 2gl
  4. 2gl

Answer

(1) 2(u2 - gl)

Solution

From the lowest point to the horizontal position the stone rises through height l.

Conservation of mechanical energy: 12mu2 = 12mv2 + mgl

⇒ v2 = u2 - 2gl

At the lowest point the velocity is horizontal; at the horizontal position it is vertical ⇒ u v

⇒ | v| = u2 + v2

= u2 + u2 - 2gl

= 2(u2 - gl)

Answer: (1)

AIPMT 2003

Keep practising — Work, Energy and Power

2

If kinetic energy of a body is increased by 300% then percentage change in momentum will be :

  1. 100%
  2. 150%
  3. 265%
  4. 73.2%
AIPMT 2002
3

250 N force is required to raise 75 kg mass from a pulley. If the rope is pulled 12 m, then the load is lifted 3 m. The efficiency of the pulley system will be

  1. 25%
  2. 33.3%
  3. 75%
  4. 90%
AIPMT 2001
4

A child is sitting on a swing. Its minimum and maximum heights from the ground are 0.75 m and 2 m respectively, its maximum speed will be

  1. 10 m/s
  2. 5 m/s
  3. 8 m/s
  4. 15 m/s
AIPMT 2001
5

Two springs A and B having spring constant KA and KB (KA = 2KB) are stretched by applying force of equal magnitude. If energy stored in spring A is EA, then energy stored in B will be

  1. 2EA
  2. EA4
  3. EA2
  4. 4EA
AIPMT 2001
6

A man is slipping on a frictionless inclined plane and a bag falls down from the same height. Then the velocity of both is related as

  1. vB > vm
  2. vB < vm
  3. vB = vm
  4. vB and vm can't be related
AIPMT 2000
7

If F = (60 i + 15 j - 3 k) N and v = (2 i - 4 j + 5 k) m/s, then instantaneous power is

  1. 195 watt
  2. 45 watt
  3. 75 watt
  4. 100 watt
AIPMT 2000
8

As shown in the figure at point O a mass is performing vertical circular motion. The average velocity of the particle is increased, then at which point will the string break [figure]

  1. A
  2. B
  3. C
  4. D
AIPMT 2000

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