Question

a boy of a mass 40 kg climbs up a stairs and reaches the roof at a height of 8 m in 5 seconds calculate the force 1) the force of gravity acting on the boy 2) the work done by him against the force of gravity 3) the power spent by the boy ( take g=10 m s–²

Answer 1

Please refer the above photograph for the used process
Hope this will be helping you.

Answer 2

mass=40kg

h=S=8m (height)

t=5sec

g=a=10m/s²

i)F=ma

=>F=mg

=>F=40×10

=>F=400N

ii)W=FS

=>W=Fh

=>W=400×8

=>W=3200J

iii)P=W/t

=>P=3200/5

=>P=640W