Work, Energy and Power · Question 56

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

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%

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%

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

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

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

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

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