Power = work done / time
work done is equal to energy
work done = 50 kJ = 50000 J
time = 2.5 s
power = 50000 J / 2.5 s
power = 20000 J/s
power = 20000 watt
1HP( horse power) = 746 watt
power in watt = 20000 /746 HP
power = 26.809 HP
so power is of 26.8 horsepower.