Question

A force of $5N$ acts on a $15kg$ body initially at rest. The work done by the force during the first second of motion of the body is

• A. $5J$
• B. $\frac{5}{6}J$
• C. $6J$
• D. $75J$

Answer 1

The correct option is B

$\frac{5}{6}J$

Step 1: Given data

Force, $F=5N$

Mass of body, $m=15kg$

Time, $t=1s$

Step 2: Finding the acceleration

$$\begin{gathered} F=ma \\ a=\frac{F}{m} \\ a=\frac{5}{15} \\ a=\frac{1}{3}m/s^2 \end{gathered}$$

Step 3: Finding displacement

$$\begin{gathered} S=ut+(1/2)a{t}^2 \\ S=0+(1/2)x(1/3)x{\left(1\right)}^2 \\ S=1/6m \end{gathered}$$

Step 4: Find work done

Work = Force * displacement produced

$$\begin{gathered} W=5x(1/6) \\ W=\frac{5}{6}J \end{gathered}$$

Hence, option B is correct.