Question

A boy does 400 j of a work in 20 s and then he does 100 j of a work in 2s find the ratio of the power delivered by the boy in two cases

Answer 1

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$\it\huge\mathfrak\red{answer:-}$]


As power=work/time

case 1: 200/10=20 watt

case 2: 100/4

= 25 watt ratio

= man/boy

= 20/25

= 4/5 = 4:5

Answer 2

» $\underline{\textbf{Power\::}}$

Rate of doing work is known as Power.

• Power = $\dfrac{work\:done}{time}$

P = $\dfrac{w}{t}$

• S.I. unit = watt

• Dimension :

Dimension of work done = [M¹L²T-²]

Dimension of time = [T¹]

So ..

Dimension of Power = $\dfrac{ {M}^{1} {L}^{2} {T}^{ - 3} }{ {T}^{1} }$

= [M¹L²T-²]

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$\underline{In\: Case\: 1}$

Work done by boy $(w_{1})$ = 400 J

Time $(t_{1})$ = 20 sec

$P_{1}$ = $\dfrac{w_{1}}{t_{1}}$

= $\dfrac{400}{20}$

= 20 watt

$\underline{In\: Case\: 2}$

Work done by boy $(w_{2})$ = 100 J

Time $(t_{2})$ = 2 sec

$P_{2}$ = $\dfrac{w_{2}}{t_{2}}$

= $\dfrac{100}{2}$

= 50 watt

Now ..

We have to find the ratio of the power delivered by boy in two cases ..

Means .. we have to find the ratio of

$\dfrac{P_{1}}{P_{2}}$

= $\dfrac{20}{25}$

= $\dfrac{4}{5}$

$\boxed{4:5}$

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