Suppose a steam locomotive is rated at 7500 horsepower. If its efficiency is 6%, how much wood must be burned in a 3-hour trip? 1 hp = 750 W. Wood has an energy density of 20.0 MJ / kg.

50,625kg of wood

Explanation:

Power input = power output : efficiency

Power output = 7500 horsepower = 7500*750W = 5625000W, efficiency = 6% = 0.06

Power input = 5625000/0.06 = 93750000W

Energy input = power input * time

time = 3hour = 3*3600 = 10800sec

Energy input = 93750000 * 10800 = 1.0125*10^12J

Mass = Energy : Energy density = (1.0125*10^12J) : (20*10^6J/kg) = 50,625kg of wood