Conservation of Momentum in Inelastic Collision

Steps:

• Identify the collision as perfectly inelastic since objects stick together.
• Note post-collision velocity is zero, so combined momentum after collision is zero.
• Apply conservation of momentum: total momentum before equals total momentum after.
• Conclude initial momenta must cancel out, summing to zero.

Why B is correct:

• Conservation of momentum law requires total initial momentum to equal final momentum of zero.

Why the others are wrong:

• A: Kinetic energy decreases in inelastic collisions as some converts to other forms.
• C: Equal masses are unnecessary; unequal masses can have equal/opposite momenta if speeds differ.
• D: Equal speeds are not required; momenta depend on mass and speed products.

Final answer: B