Question

Please give clear answer.

A boy weighing 40kg carries a box weighing 20kg to the top of a building 15m high in 25 seconds. Calculate the power, ( Take g = 10m/s^2 ).

Answer 1

$\huge{\bold{\underline{\underline{....Answer....}}}}$

$\huge{\bold{\underline{Given:-}}}$

• Mass of the boy (M) = 40 Kg.
• Mass of the box (m) = 20 Kg.
• Height of the building (h) = 15 m.
• Time (t) = 25 Seconds.

$\huge{\bold{\underline{Explanation:-}}}$

Total mass of the system (M')

$\large{\bold{M' = M + m}}$

Substituting the values,

$\large{M' = 40 + 20}$

$\large{M' = 60 \: Kg}$

Now, Work done by the boy,

$\large{\bold{W = mgh}}$

Substituting the values,

$\large{W = 60 \times 10 \times 15}$

$\large{W = 900 \times 10}$

$\large{\boxed{W = 9000 \: J}}$

So, the work done by the boy is 9000J.

Now, Power,

As we know,

Power :-

Power is defined as Rate of doing work by a body.

$\large{\bold{P = \dfrac{W}{t}}}$

Substituting the values,

$\large{P = \dfrac{9000}{25}}$

$\large{P = \dfrac{ \cancel{9000}}{ \cancel{25}}}$

$\huge{\boxed{\boxed{P = 360 \: Watts}}}$

So,the power executed by the boy is 360 watts.

Answer 2

$\huge\underline\mathfrak\blue{Answer-}$

Power = 360 W

_____________________

$\huge\underline\mathfrak\blue{Explanation-}$

We know that,

Power = $\frac{Work}{time}$

Also, Work = Force × displacement

=> So, we have to calculate the force firstly,

Force = mass × acceleration ( due to gravity )

Put the given values,

=> Force = 60 × 10 = 600 N

_____________________

Now,

Work = $\frac{600}{25}$ => 9000 J

______________________

Power = $\frac{Work}{time}$

put work = 9000 J and time = 25 s

power = $\frac{9000}{25}$

$\therefore$ $\huge\boxed{Power\:=\:360\:W}$