Answer:
You input potential energy into the rubber band system when you stretched the rubber band back. Because it is an elastic system, this is kind of potential energy is specifically called elastic potential energy.
Answer:
Part a)

Part b)

Part c)

Explanation:
Part a)
As we know that the speed of light is given as


now the frequency of the light is given as

so we have


Part b)
Position of Nth maximum intensity on the screen is given as

so here we know for 3rd order maximum intensity

n = 3
L = 1.4 m


Part c)
angle of third order maximum is given as



At the end of the baseball bat, because with the length of the bat he had a longer reach and the end of the bat was moving faster than his hands were