Q. A wagon weighing $1000\ kg$ is moving with a velocity $50\ km/h$ on smooth horizontal rails. A mass of $250\ kg$ is dropped into it. The velocity with which it moves now is
A) $2.5\ km/hour$
B) $20\ km/hour$
C) $40\ km/hour$
D) $50\ km/hour$
Explanation
(c) According to principle of conservation of linear momentum $1000 \times 50 = 1250 \times v \Rightarrow v = 40\ km/hr$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.