Question

A boy weighing 40 kgf climbs up a stair of 30 steps each 20 cm high in 4 minutes and a girl weighing 30 kgf does the same in 3 minutes. Compare:

1. The work done by them.
2. The power developed by them.

Answer 1

(i) Weight of boy = Force = 40 kgf

Distance travelled in climbing 30 steps each

20 cm high = 30 × 20 = 600 cm = 6 m

Work done in 4 min = W = F × S

= 40 × 6 = 240

Weight of girl = Force = 30 kgf

Distance covered in 3 min = 6 m

∴ Work done in 3 min. = F × S

= 30 × 6

= 180 N

∴ Ratio of work done = 240 : 180 = 4 : 3

(ii) Power = `"W"/"T"`

Power developed by

Boy : Girl

⇒ `240/4 : 180/3`

⇒ 60 : 60 

⇒ 1 : 1