(a) Find the useful power output (in W) of an elevator motor that lifts a 2800 kg load a height of 30.0 m in 12.0 s, if it also increases the speed from rest to 4.00 m/s. Note that the total mass of the counterbalanced system is 10,000 kg-so that only 2800 kg is raised in height, but the full 10,000 kg is accelerated. (Enter a number.) W (b) What does it cost (in cents), if electricity is $0.0900 per kW . h? (Enter a number.) cents