Question

a man has power of 90w and mass 60kg runs up a staircase in 40 seconds. if each step of staircase is 20cm high calculate the number of steps?

Answer 1

we know....power = energy / time
m = 60 kg
g = 10 m/s
h = ?
energy = P.E = mgh
= 60 × 10 ×h
= 600 h
power = 90W
time = 40 sec
90 W = 600 h ÷ 40 sec
600 h = 40 ×90
h = 3600 ÷ 600
h = 6 metres = 600 cm
height of 1 step = 20 cm
height of steps the man ran = 600 cm
no  of steps = 600 ÷ 20
∴ 30 steps

Answer 2

Hi friend,

M = 60kg
g =10
h = x no of steps
Let no of steps be x
So, height = 20cm x
= 0.2 x

Power = work done / time
m.g.h/t
60*10*0.2x/40 =90
120x/40 =90
3x = 90
X = 90/3x = 30 steps

Hope this helps u
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