Question

A body of mass $10\text{kg}$ is moving with a constant velocity $10\text{m/s}$. When a constant force acts for $4\text{s}$ on it, it moves with a velocity $2\text{m/s}$ in the opposite direction. The magnitude of force acting on the body is

• A. $10\text{N}$
• B. $30\text{N}$
• C. $45\text{N}$
• D. $50\text{N}$

Answer 1

The correct option is B $30\text{N}$

Here initial velocity $=u=10\text{m/s}$
Final velocity $=v=-2\text{m/s}$
($\because$ opposite direction)
Change in velocity $(v-u)=-2-10=-12\text{m/s}$;
We know that, $a=\frac{v-u}{t}$
$\Rightarrow a=-\frac{12}{4}=-3{\text{m/s}}^2$
Force acting on body, $F=ma=10\times (-3)=-30\text{N}$
Magnitude, $F=30\text{N}$