An automobile travelling with speed of 60 km/h, can brake to sto

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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

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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


D.

60 m

Third equation of motion gives
v2 = u2 + 2as ⇒ 2
s ∝ u (since v = 0)
where a = retardation of body in both the cases

therefore, straight s subscript 1 over straight s subscript 2 space equals space fraction numerator straight u subscript 1 superscript 2 over denominator straight u subscript 2 superscript 2 end fraction .... (i)

Here, s1 = 20 m, u1 = 60 km/h, u2 = 120 km/h. Putting the given values in eq. (i), we get

20 over straight s subscript 2 space equals space open parentheses 60 over 120 close parentheses squared
space straight s subscript 2 space equals space 20 space straight x space open parentheses 120 over 60 close parentheses squared
space equals space 20 space straight x space 4 space
space equals space 80 space straight 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

543 Views

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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