Hello. I have questions about physics.

Josh sleds down a hill from a height of 35 m. He has a mass of 60 kg. He starts from rest at the top of the hill.

a. If there were no friction, how fast would he be going when he reached the bottom of the hill?

b. In reality, the friction between the sled and the ground causes Josh to lose 15% of his initial energy as heat. In this case, how fast will he be going when he reaches the bottom?

c. Josh is sledding into a valley that rises again on the other side. He can sled down one side and then back up the other side. If he loses 15% of his initial energy to friction by the time he reaches the bottom, then loses another 10% of his remaining energy sledding back up, how high can he slide up the other side of the valley before he comes to a stop?

d. Instead of starting from rest, Josh starts with a speed of 10 m/s. How fast will he be going when he reaches the bottom of the hill? (Assume no friction.)