Question

A boy mass 30Kg can go up 20 steps each of height 10cm in 20sec. Calculate the power of the boy. [g=9.8m/s²]​

Answer 1

Required Answer:-

Power is the rate of work done. Here, Let's see what is provided to us:

• Mass(m) = 30 kg
• No. of steps = 20
• Height of each step = 10 cm
• g = 9.8 m/s²
• Time taken(t) = 20 s

Total height:

= 20 × 10 cm

= 200 cm i.e. 2 m

Work done is given by:

$= \large{ \boxed{ \rm{mgh}}}$

Then, Power of the boy:

$= \large{ \boxed{ \rm{ \frac{mgh}{t}}}}$

Plugging all the values,

P = mgh/t

P = 30 × 9.8 × 2 / 20 J/s

P = 9.8 × 3 J/s

P = 29.4 J/s

Hence,

The power of the boy is 29.4 J/s or 29.4 W

Note:-

• Take care of all the units expressed in the same system i.e. SI units (preferred).
• Finally add the unit of the resultant quantity in the same system.

Answer 2

Answer:

Given :-

Mass = 30 kg

Steps = 20

Height = 10 cm

Time = 20 sec

To Find :-

Power

Solution :-

The total height of travelled by boy = 10 × 20

= 200 cm

1 m = 100 cm

200 cm = 200/100 = 2 m

Now,

Power = mgh/t

Power = 30 × 9.8 × 2/20

Power = 30 × 9.8/10

Power = 3 × 9.8

Power = 29.4 Watt