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In that same spring-loaded cart collision, the internal kinetic energy before impact is 0.763 J and after impact is 6.22 J. What does this change tell you about the collision?
AIt is elastic, since kinetic energy changed but momentum was conserved
BIt is inelastic, since the spring added internal kinetic energy instead of removing it
CIt must be an error, since internal kinetic energy can never increase in a collision
DIt is perfectly inelastic, since the two carts moved off with the same final velocity
Answer & Solution
Correct answer: B. It is inelastic, since the spring added internal kinetic energy instead of removing it
1. An elastic collision requires internal kinetic energy to stay the same, but here it rises from 0.763 J to 6.22 J, so the collision is inelastic.
2. Inelastic collisions are usually associated with energy loss, but the definition only requires that internal kinetic energy is not conserved, in either direction.
3. The spring's stored potential energy converts into internal kinetic energy during the collision, which is why the total increases.
4. The two carts end this collision with different final velocities, -4.00 m/s and 3.70 m/s, so they clearly have not stuck together, ruling out a perfectly inelastic description.
_Source: OpenStax College Physics (CC BY 4.0), Ch 8 "Linear Momentum and Collisions", section 8.5 Inelastic Collisions in One Dimension_
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