Question

A $500$ kg rolling boxcar has a velocity of $5m/s$. When it strikes another boxcar of the same mass that is at rest, both cars stick together and continue to roll down the track with a momentum of:

• A. $0kg\cdot m/s$
• B. $3125kg\cdot m/s$
• C. $6250kg\cdot m/s$
• D. $12,500kg\cdot m/s$
• E. $2500kg\cdot m/s$

Answer 1

Answer: (E)

$2500kg\cdot m/s$

In a collision (elastic or inelastic) the momentum is conserved.

Momentum in the given question before collision, $p=mv=500\times 5=2500kgm/s$

Due to conservation law the momentum after collision must be equal to $2500kgm/s$