Question 41

The front car speeds up and the rear car slows down.

In a completely elastic collision, both momentum and kinetic energy are conserved. When the rear car, traveling faster, collides with the front car, it transfers some of its energy to the front car, causing it to speed up while the rear car slows down.

A) The front car speeds up and the rear car slows down.

This option is correct because, in an elastic collision, the faster rear car imparts some of its kinetic energy to the slower front car. Consequently, the front car gains speed while the rear car experiences a decrease in speed.

B) Both cars speed up.

This option is incorrect. For both cars to speed up, the rear car would need to impart energy without losing any, which contradicts the principles of momentum and energy conservation in a collision. The rear car must lose speed for energy to be transferred to the front car.

C) The front car slows down and the rear car speeds up.

This option is incorrect. In an elastic collision, the faster rear car cannot cause the front car to slow down while it speeds up. The conservation of momentum dictates that the rear car must slow down as it transfers energy to the front car, which speeds up.

D) Both cars slow down.

This option is incorrect. While it may seem plausible that both cars slow down after the collision, the dynamics of an elastic collision indicate that the front car must gain speed from the rear car's loss of speed. Therefore, only the rear car slows down.

Conclusion

The correct answer, that the front car speeds up while the rear car slows down, is consistent with the laws of conservation of momentum and kinetic energy in elastic collisions. All other options fail to accurately describe the energy transfer and velocity changes that occur during such a collision scenario.