Question

A force causes a $10kg$ body to double it’s velocity in four seconds. If the final velocity of the body is $7.2m{s}^{-1}$, calculate the magnitude of the force.

• A. $8.6N$
• B. $9N$
• C. $6.8N$
• D. $12.4N$

Answer 1

The correct option is B $9N$

Given: mass, $m=10kg$, initial velocity, $u=3.6m{s}^{-1}$ (initial velocity is half of final velocity), final velocity, $v=7.2m{s}^{-1}$, and time, $t=4s$.
Let the acceleration of the body be 'a'.

Using first equation of motion:
$v=u+at\Rightarrow a=\frac{v-u}{t}=\frac{7.2-3.6}{4}$
$\Rightarrow a=0.9m{s}^{-2}$

Using Newton’s second law of motion:
Force, $F=ma=10\times 0.9=9N$
Therefore, the magnitude of the force is $9N$