Question

A machine which is 75 percent efficient, uses 12 joules of energy in lifting up a 1 kg mass through a certain distance. The mass is then allowed to fall through that distance. The velocity at the end of its fall is (in m/s)

• A. $\sqrt{24}$
• B. $\sqrt{32}$
• C. $\sqrt{18}$
• D. $\sqrt{9}$

Answer 1

The correct option is C $\sqrt{18}$

Potential energy of a body = 75 $\%$ of 12 J
$mgh=9J\Rightarrow h=\frac{9}{1\times 10}=0.9m$
Now when this mass allow to fall then it acquire velocity
$v=\sqrt{2gh}=\sqrt{2\times 10\times 0.9}=\sqrt{18}m/s$.