A constant retarding force of 50N is applied to a body of mass 20kg moving with the speed of 15m/s. How long does the body take to stop?

Ans1 Given

F=50N

M=20kg

u=15m/s

v=0

As F=ma

a=50/20=2.5m/s^2

Since the retarding is negativd so -2.5 m/s^2

Time=

v=u+at

=0-15/-2.5=6s

Ans2 F=ma

50=20×0-15/t

50=20×-15/t

50/20×-15=1/t

-6 s=t

Why the 2 is incorrect ?

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Solution

It is because you should take force as - 50 and not +50 as it is deceleration.

By doing so, you're answer will be correct.

Hope this helps .

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It is because you should take force as - 50 and not +50 as it is deceleration. By doing so, you're answer will be correct. Hope this helps .

It is because you should take force as - 50 and not +50 as it is deceleration.

By doing so, you're answer will be correct.

Hope this helps .