a parent pulls a sled and rider with a combine weight of 50kg up a 20-meter high hill and then gives the sled a push, providing an initial velocity of 4m/s. Frictional forces acting on the sled do 2000 joules of negative work as the sled moves down the hill. Find the total energy of this system.

Which of the following correctly describes what happens when an atomic bomb explodes? small pieces of fissionable material are joined and form a body with a mass greater than the critical mass, the relative number of neutrons escaping decreases, and a chain reaction and explosion result. large pieces of fissionable matter are brought together quickly and form a body with a mass smaller than the critical mass, the relative number of escaping neutrons increases, and a chain reaction and explosion result.