Laws Of Motion Question 172

Question: A body of mass 2 kg moving on a horizontal surface with an initial velocity of 4 m/sec comes to rest after 2 sec. If one wants to keep this body moving on the same surface with a velocity of 4 m/sec, the force required is[NCERT 1977]

Options:

A) 8 N

B) 4 N

C) Zero

D) 2 N

Show Answer

Answer:

Correct Answer: B

Solution:

$ u=4\ m/s $ , $ v=0,\ t=2\sec $

$ v=u+at $

therefore $ 0=4+2a $

therefore $ a=-2m/s^{2} $

$ \therefore $ Retarding force$ =ma=2\times 2=4 $ N This force opposes the motion. If the same amount of force is applied in forward direction, then the body will move with constant velocity.



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