One model of tennis ball launcher has advertised that it is capable of imparting 15,000 J of kinetic energy to a 0.5 kg ball initially at rest. A
student carefully measures the compression of the spring to be 0.10 m-
What is the value of the spring constant for the tennis ball launcher
according to the data provided?

The answer for the first question is: 3,000,000 N/m

The answer for the second question is: If the question was, "Which of the following is the best example of kinetic energy being transformed into potential energy?" then the answer is winding the spring on a toy car

Explanation:

For the first question: I have no explanation, I just got it right on my test so I thought i'd help you out.

For the second question: (i'll try to explain the best I can).

Kinetic energy = energy in motion

Potential energy = stored energy

so when winding the spring of a car you are using energy in motion (kinetic energy) to create stored energy (potential energy) that will be used to move the car. So it goes something like:

kinetic energy > potential energy > kinetic energy

0.19 m/s and 0.45 m/s