A book with a mass of 1.8 kg sits on a bookshelf. If it has a gravitational potential energy of 42 J, how high is the shelf? The acceleration of gravity is
9.8 m/s2

A1500 w electric heater is plugged into the outlet of a 120 v circuit that has a 20 a circuit breaker. you plug an electric hair dryer into the same outlet. the hair dryer has power settings of 600 w, 900 w , 1200 w, and 1500 w. you start with the hair dryer on the 600 w setting and increase the power setting until the circuit breaker trips. under what setting does the circuit breaker trip.