Question

A force of $5N$ is applied on a $20kg$ mass at rest. the work done in the third second is:-

• A. $\frac{25}{8}J$
• B. $\frac{25}{4}J$
• C. $12J$
• D. $25J$

Answer 1

The correct option is A $\frac{25}{8}J$

Displacement in third second = displacement till 3rd second - Displacement till 2nd second

=$\frac{a}{2}{3}^2-\frac{a}{2}{2}^2=\frac{5}{8}m$ (No term of ut because u=0)

Thus work done in third second =$5\times \frac{5}{8}=\frac{25}{8}J$