Question 20 of 210

Force acts for $20s$ on a body of mass $20kg$, starting from rest, after which the force ceases and then body describes $50m$ in the next $10s$. The value of force will be :

A$40N$B$5N$C$20N$D$10N$

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Answer: (B) $5N$

For the second case when body is moving with constant velocity, we can write
$50=V\times 10$
$\Rightarrow V=5m{s}^{-1}$
Now this velocity if the final velocity for the first case, therefore
$V=0+a\times 20$
$\Rightarrow 5=a\times 20$
$\Rightarrow a=\dfrac{1}{4}m{s}^{-2}$
Hence, required force will be
$F=ma=20\times \dfrac{1}{4}=5N$