Question

A force of $20N$ acting on a body of mass $10kg$ is found to double its velocity in $8s$. Find its initial velocity.

• A. $4m{s}^{-1}$
• B. $8m{s}^{-1}$
• C. $32m{s}^{-1}$
• D. $16m{s}^{-1}$

Answer 1

The correct option is D $16m{s}^{-1}$

Given: force $F=20N$, mass $m=10kg$ and time $t=8s$.
Let initial velocity be $u$, acceleration be $a$ and as body double its velocity in $8s$, final velocity, $v=2u$.
From, Newton's second law ,we know $F=ma=m\left(\frac{v-u}{t}\right)$
Substituting the values, we get,
$20=10\left(\frac{v-u}{t}\right)$
$2=\frac{2u-u}{8}(\because v=2u)$
$\Rightarrow$$u=16m{s}^{-1}$
Therefore, initial velocity is $16m{s}^{-1}$