Physics

Physics

Problem

A 0.20 kg0.20\,\text{kg} glider traveling at 0.80 m/s0.80\,\text{m/s} on a frictionless air track collides elastically and head-on with a second glider of unknown mass that is initially at rest. After the collision, the 0.20 kg0.20\,\text{kg} glider reverses direction and moves at 0.20 m/s0.20\,\text{m/s}. What is the mass of the second glider? a) 0.25 kg0.25\,\text{kg} b) 0.33 kg0.33\,\text{kg} c) 0.12 kg0.12\,\text{kg} d) 0.40 kg0.40\,\text{kg}
Intuitive explanation

In an elastic collision, both momentum and kinetic energy are conserved—two equations that work together to constrain the outcome. Since the first glider bounced backward (reversed direction), you know the second glider must be heavier; use the momentum equation to find the second glider's velocity after collision, then apply energy conservation to solve for its mass. The key is recognizing that the reversal tells you something crucial about the mass ratio.

Intuitive explanation

In an elastic collision, both momentum and kinetic energy are conserved—two equations that work together to constrain the outcome. Since the first glider bounced backward (reversed direction), you know the second glider must be heavier; use the momentum equation to find the second glider's velocity after collision, then apply energy conservation to solve for its mass. The key is recognizing that the reversal tells you something crucial about the mass ratio.

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