Question

A thin uniform straight rod of mass 2 kg and length 1 m is free to rotate about its upper end when at rest. It receives an impulsive blow of 10 Ns at its lowest point, normal to its length as shown in figure. The kinetic energy of rod just after impact is

• A. 75 J
• B. 100 J
• C. 200 J
• D. none

Answer 1

The correct option is A

75 J

Using Angular impulse- Angular momentum theorem
(10 l)=Iw - 0

$10=\frac{2\times 1^2}{3}W\Rightarrow w=15rad{s}^{-1}\text{We have,}K=\frac{1}{2}I{w}^2=\frac{1}{2}\times \left(\frac{2\times 1^2}{3}\right)\times {15}^2=\frac{225}{3}=75J$