can someone walk me through this physics problem?

Question

1. what will the kinetic energy of an arrow having a potential energy of 50 J after it is shot from a bow?

also.

2. a boulder is raised above the ground so that its potential energy relative to the ground is 200 J. Then it is dropped. What is its kinetic energy just before it hits the ground?

thanks so much

Answer 1

1. The potential energy of the system is from the tension in the bowstring. When the arrow is released all of that potential energy is converted into kinetic energy. So the arrow gets all 50J of energy.

2. Again, all of the gravitational potential energy of the system is converted to kinetic. The boulder has 200 J of kinetic energy just before it hits the ground.