Q. A mass of 50 kg is raised through a certain height by a machine whose efficiency is 90%, the energy is 5000 J. If the mass is now released, its KE on hitting the ground shall be
A) 5000 J
B) 4500 J
C) 4000 J
D) 5500 J
Explanation
(b) Because the efficiency of machine is 90%, hence, potential energy gained by the mass
$= \frac{90}{100} \times$ energy spend $= \frac{90}{100} \times 5000 = 4500\ J$
When the mass is released now, gain in KE on hitting the ground
$=$ Loss of potential energy
$= 4500\ J$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.