Question

A boy of weight 40kgf climbs up the 15 steps ,each 15 cm high in 10s and a girl of weight 20kgf does the same in 5s .compare :(I) the work done ,and (ii) the power devolped by them .take g= 10N/kg .

Answer 1

refer. to book icse class 10th for any doubts of.25. chapter-Work,energy and power ...

Answer 2

Answer:

The work done by them is 2:1 and The power developed by them is 1:1.

Explanation:

Given that,

Weight of the boy = 40 kgf

Time taken by the boy = 10 s

Weight of the girl = 20 kgf

Time taken by the girl = 5 s

Distance covered by both in 15 cm steps is

$D = 15\times15$

$D= 225\ cm$

(I). The work done

The work done by the boy in climbing the stairs is

$W= F\times D$

$W_{b}=40\ kgf\times 225\ cm$

$W_{b}= 9000\ J$

The work done by the girl in climbing the stairs is

$W= F\times D$

$W_{g}=20\ kgf\times 225\ cm$

$W_{g}= 4500\ J$

The work done by them

$\dfrac{W_{b}}{W_{g}}=\dfrac{9000}{4500}$

$\dfrac{W_{b}}{W_{g}}=\dfrac{2}{1}$

Therefor,

The work done by them is 2:1

(II). The power developed is

The power developed by the boy

$P_{b} =\dfrac{W}{t}$

$P_{b}=\dfrac{9000}{10}$

$P_{b}=900 W$

The power developed by the girl

$P_{g} =\dfrac{W}{t}$

$P_{g}=\dfrac{4500}{5}$

$P_{g}=900 W$

The power developed by them

$\dfrac{P_{b}}{P_{g}}=\dfrac{900}{900}$

Therefore,

The power developed by them is 1:1.

Hence, The work done by them is 2:1 and The power developed by them is 1:1.