A ball is released from the top of a tower of height h metres. I

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 Multiple Choice QuestionsMultiple Choice Questions

31.

Consider a car moving on a straight road with a speed of 100 m/s. The distance at which car can be stopped is [µ =k 0.5]

  • 800 m

  • 1000 m

  • 600 m

  • 600 m

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32.

A ball is released from the top of a tower of height h metres. It takes T seconds to reach the ground. What is the position of the ball in T/3 seconds?

  • h/9 metres from the ground

  • 7h/9 metres from the ground

  • 8h/9 metres from the ground

  • 8h/9 metres from the ground


C.

8h/9 metres from the ground



second law of motion
straight s space equals ut space plus space 1 half space plus gT squared
or space straight h equals 0 plus 1 half gT squared space left parenthesis because space straight u equals 0 right parenthesis
therefore space straight T equals square root of open parentheses fraction numerator 2 straight h over denominator straight g end fraction close parentheses end root
At space straight t space equals space straight T over 3 straight s comma
straight s space equals space 0 plus space 1 half straight g space open parentheses straight T over 3 close parentheses squared
rightwards double arrow space straight s space equals space 1 half space straight g. straight T squared over 9
rightwards double arrow space straight s space equals space straight g over 18 space straight x space fraction numerator 2 straight h over denominator straight g end fraction space space space space open parentheses therefore space equals space square root of fraction numerator 2 straight h over denominator straight g end fraction end root close parentheses
therefore s = h/9 m
Hence, the position of ball from the ground= h- h/9 = 8h/9 m

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33.

An automobile travelling with speed of 60 km/h, can brake to stop within a distance of 20 cm. If the car is going twice as fast, i.e 120 km/h, the stopping distance will be

  • 20 m

  • 40 m

  • 60 m

  • 60 m

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34.

A machine gun fires a bullet of mass 40 g with a velocity 1200 ms−1. The man holding it can exert a maximum force of 144 N on the gun. How many bullets can he fire per second at the most?

  • one 

  • Four

  • Two

  • Two

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35.

Two masses m1 = 5 kg and m2 = 4.8 kg tied to a string are hanging over a light frictionless pulley. What is the acceleration of the masses when lift free to move?
(g = 9.8 m/s2 )

  • 0.2 m/s2

  • 9.8 m/s2

  • 5 m/s2

  • 5 m/s2

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36.

A block rests on a rough inclined plane making an angle of 30° with the horizontal. The coefficient of static friction between the block and the plane is 0.8. If the frictional force on the block is 10 N, the mass of the block (in kg) is (take g = 10 m/s2 )

  • 2.0

  • 4.0

  • 1.6 

  • 1.6 

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37.

It is found that if a neutron suffers an elastic collinear collision with deuterium at rest, fractional loss of its energy is pd; while for its similar collision with carbon nucleus at rest, fractional loss of energy is pc. The values of pd and pc are respectively :

  • (0,1)

  • (.89,.28)

  • (.28,.89)

  • (0,0)


38.

The one which does not represent a force in any context is

  • Friction

  • Impulse

  • Tension 

  • Weight


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39.

Water from a hose pipe of radius 5 cm strikes a wall normally at a speed of 5 ms-1. The force exerted on the wall in newton is

  • 13.5 π

  • 6.25 π

  • 62.5π

  • 27π


40.

A stone of density 2000 kg m-3 completely immersed in a lake is allowed to sink from rest. If the effect of friction is neglected, then after 4 seconds, the stone will reach a depth of

  • 78.4 m

  • 39.2 m

  • 19.6 m

  • 9.8 m


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