A 5 kg book is held 20 m above the floor. How much gravitational potential energy does it have?*

(* USE 10 /s2 as the acceleration due to gravity)

a 100 J
b 4 J
c 1000 J
d 98 J

Ahot-air balloon is 11.0 m above the ground and rising at a speed of 7.00 m/s. a ball is thrown horizontally from the balloon basket at a speed of 9.00 m/s. ignore friction and air resistance and find the speed of the ball when it strikes the ground.