Question

A body of mass 5 kg has momentum of 10 kg m/sec. When a force of 0.2 N is applied on it for 10 sec, the change in its kinetic energy is:

• A. 4.4 J
• B. 3.3 J
• C. 5.5 J
• D. 1.1 J

Answer 1

The correct option is A 4.4 J

Change in momentum, $\Delta p=F.t=0.2\times 10=2$
Initial value of velocity $=\frac{10}{5}=2m/sec$
Initial energy $=\frac{1}{2}\times 5\times 2\times 2=10J$
Total final momentum $=10+2=12kgm/sec$
Final velocity $=\frac{12}{5}m/sec$
Final energy $=\frac{1}{2}\times 5\times \frac{12}{5}\times \frac{12}{5}$
$=\frac{72}{5}=14.4J$
Change in energy $=14.4-10=4.4joule$