A student of mass 50 kg climbs a staircase of vertical height 2.4 m in 6.0 s. Gravitational field strength is 10 N/kg. What is the mean useful power output?
83 W83\ \mathrm{W}83 W
200 W200\ \mathrm{W}200 W
1200 W1200\ \mathrm{W}1200 W
20 W20\ \mathrm{W}20 W