Which type of energy is stored while stretching the catapult? How this energy is obtained?
While stretching the catapult, potential energy is stored in it. This energy is obtained by doing work against the restoring force of the string.
The potential energy of an object kept on the surface of the earth is zero, why? Give reason
The potential energy of an object kept on the Earth's surface is 0 because it has not been displaced to any height.
We know, Potential Energy (PE) = mgh
At the surface of the Earth, h = 0
So, PE = mg * 0
= 0