Power of pump = P = 0.5 hp = 0.5 *746 W = 373 watts , ( 1 hp =746 watts)
h = height = 10m
g= 10m/s^2
t = time taken = 49 seconds
we will use formula , ( power = work / time ) to find work.
work = power x time = 373 * 49 =18,277 joules
now work done by pump = potential energy gaine by water = m*g*h
or m = work / (g*h) = 18,277/ (10*10) =182.77 kg
so mass of water = 182.77 kg