Given :
Initial speed of car A is 15 m/s and initial speed of car B is zero.
Final speed of car A is zero and final speed of car B is 10 m/s.
To Find :
What fraction of the initial kinetic energy is lost in the collision.
Solution :
Initial kinetic energy is :

Final kinetic energy is :

Now, fraction of initial kinetic energy loss is :

Therefore, fraction of initial kinetic energy loss in the collision is 1.25 .
The fraction of energy that is lost is 25%, it depends how fast the ball was going until it lost 25% of its energy, the gravitational energy was transferred into the kinetic energy that helped the ball bounce back
Answer:
It says that momentum cannot be created or destroyed. Momentum just passes through systems as opposed to just disappearing in thin air. Momentum can be changed to heat or energy.
Explanation:
Since the car is at rest, the force experienced by car will be normal face(exerted by surface to which car is in contact) and weight of the car.
As the car is at rest, net force on the car should be zero.