Two collisions are carried out to crash-test a \(1000-\mathrm{kg}\) car.

(a) While moving at \(15 \mathrm{mi} / \mathrm{h}\), the car strikes an identical car initially at rest.

(b) While moving at \(15 \mathrm{mi} / \mathrm{h}\), the car strikes an identical car moving toward it and also traveling at \(15 \mathrm{mi} / \mathrm{h}\). For each collision, how much kinetic energy can be converted to internal energy, and what fraction of the initial kinetic energy of the two-car system does this represent?