Q. A metal ball of mass $2\ kg$ moving with a velocity of $36\ km/h$ has an head on collision with a stationary ball of mass $3\ kg$. If after the collision, the two balls move together, the loss in kinetic energy due to collision is
A) $40\ J$
B) $60\ J$
C) $100\ J$
D) $140\ J$
Explanation
(b) $v = 36\ km/h = 10\ m/s$
By law of conservation of momentum
$2 \times 10 = (2 + 3)V \Rightarrow V = 4\ m/s$
Loss on K.E. $= \frac{1}{2} \times 2 \times (10)^{2} - \frac{1}{2} \times 5 \times (4)^{2} = 60\ J$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.