Question

A 25 N force is applied to a 3 kg box initially at rest. After 20 meters, how fast is the box moving ?

Answer 1

Given data:

$\begin{gathered} F=25\text{ N} \\ m=3\text{ kg} \\ s=20\text{ m} \\ u=0\text{ m/s (as the box is initially at rest)} \end{gathered}$

The force acting on the box is given as,

$F=ma$

Here, a is the acceleration of the box.

Rearranging the equation in order to get the acceleration of the box;

$a=\frac{F}{m}$

Substituting the known values;

$\begin{gathered} a=\frac{25\text{ N}}{3\text{ kg}} \\ =8.33\text{ m/s}^2 \end{gathered}$

The third equation of motion is given as,

$v^2=u^2+2as$

Substituting the known values,

$\begin{gathered} v^2=(0)^2+2\times(8.33\text{ m/s}^2)\times(20\text{ m) } \\ v^2=333.2 \\ v=\sqrt[]{333.2} \\ =18.25\text{ m/s} \end{gathered}$

Therefore, the velocity of box after 20 m is 18.25 m/s.