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A boy of mass 40kg climbs up the stairs and reaches the roof at a height 8m in 5 s. Calculate:
A boy of mass 40kg climbs up the stairs and reaches the roof at a height 8m in 5 s. Calculate:
Class 10 | ICSE | Physics | Selina | Work Energy
A boy of mass 40kg climbs up the stairs and reaches the roof at a height 8m in 5 s. Calculate:

(i) The force of gravity acting on the boy,

(ii)The work done by him against gravity,

(iii)The power spent by the boy.

(take g= 10ms-2)

Solutions:

According to the question –

Mass of a boy is 40 kg

Vertical height moved by the boy is h = 8 m

Time taken by the boy is t = 5 s

(i) Force of gravity acting on the boy is given by the expression –

F = mg = 40 × 10

F = 400 N

(ii) Now, we have to determine the work done by a boy against the force of gravity while climbing,

Work done by a boy = Force × distance moved in the direction of force = F × S

W = 400 × 8

Therefore, W = 3200 J

(iii) Power spent is given as follows –

Power = (work done / time taken) = 3200 / 5

Power = 640 W

i

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