Question

A man has a power of 90 watt and mass of 60kg runs up a staircase in 40 seconds . If each step of staircase is 20 cm high, calculate the number of steps.

Answer 1

Power ,P = 90 W

Mass , m = 60 kg

Time , t = 40 sec

As we all know ,
Power = Energy / time

Power = mgh / time

90 = 60 × 10 × h / 40
90 × 40 = 600 h
3600 = 600 h
h = 3600 / 600
h = 6 metre

Thus total height of steps the man covered = 6 m = 600 cm

We are given the height of one step and total height of steps he ran.
Thus its simple that no: of steps the man went up = Total height of steps / Height of one step


Height of one step = 20 cm

Total height of steps = 600 cm

No : of steps he ran = 600 / 20 = 30 steps
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plz mark brainliest ....

Answer 2

Hi @Govind 

Power (P) = 90 W

Mass(m) = 60 Kg

Time(T) = 40s

So, Power = $\frac{Energy}{Time}$ __________ (1)

But Energy = mgh _______(2)

By putting (2) in (1) We get

Power = $\frac{mgh}{Time}$

So, 90 = $\frac{60*10*h}{40}$      { Taking g = 10 }

90*40 = 600h
3600 = 600h
$\frac{3600}{600}$ = h

h = 6m or h = 600

So we have the Total Height of steps and the Height of one slop is also given. So, to calculate how much steps he ran Just divide Height of total no. of steps to Height of one step.

So, Height of one step = 20 cm

Total Height of steps = 600 cm 

So, No. of steps he ran =  $\frac{Total Height of step}{Height of one step}$

= $\frac{600}{20}$
= 30 steps 

So He ran 30 steps 

Hope you got your answer. :)