A 1200-kg frictionless roller coaster starts from rest at a height of 24 m. What is its kinetic energy when it goes over a hill that is 12 m high?A radio-controlled car increases its kinetic energy from 4 J to 12 J over a distance of 2 m. What was the average net force on the car during this interval?Valerie is able to do 1200 joules of work in 10 seconds. Brett is able to do 5000 joules of work in 50 seconds. Who is more powerful?