Question

A constant force acting on a body of mass $3.0\text{kg}$ changes its speed from $2.0\text{m/s}$ to $3.5\text{m/s}$ in $25$ seconds. The direction of the motion of the body remains unchanged.
What is the magnitude and direction of the force?

• A. $0.018N$, opposite to direction of motion.
• B. $0.18N$, opposite to direction of motion.
• C. $0.018N$, along direction of motion.
• D. $0.18N$, along direction of motion.

Answer 1

The correct option is D $0.18N$, along direction of motion.

Mass of the body $m=3.0\text{kg}$,
Time taken $t=25$ seconds
Initial velocity, $u=2\text{m/s}$,
Final velocity, $v=3.5\text{m/s}$
Putting values in relation $v=u+at$, we get
$3.5=2.0+a\times 25\Rightarrow 25a=3.5-2.0=1.5$
$\Rightarrow a=\frac{1.5}{25}=0.06{\text{m/s}}^2$

$\therefore$ Force, $F=m\times a=3.0\times 0.06=0.18\text{N}$
As velocity is increasing, direction of force is along direction of motion.