Q. A mass of $20\ kg$ moving with a speed of $10\ m/s$ collides with another stationary mass of $5\ kg$ As a result of the collision, the two masses stick together. The kinetic energy of the composite mass will be
A) $600\ Joule$
B) $800\ Joule$
C) $1000\ Joule$
D) $1200\ Joule$
Explanation
(b) $m_{1}v_{1} + m_{2}v_{2} = \left( m_{1} + m_{2} \right)v_{sys.}$
$20 \times 10 + 5 \times 0 = (20 + 5)v_{sys.} \Rightarrow v_{sys.} = 8\ m/s$
K. E. of composite mass $= \frac{1}{2}\ (20 + 5) \times (8)^{2} = 800\ J$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.