A girl of mas 40 kg
runs a height of 80 stairs, each 25 cm high with
a load of
of 20 kg on her head in 25s. If g is 10 m/s2
Gravitational force acting on the girl.
(11) Work done by her.
(ii) Useful work done by the her.
(iv) Her power in watt.
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(i) Gravitational force acting on the girl = Her mass in kg x g
= 40 x 10 = 400 N
(ii) Total gravitational force = (Mass of girl + load) x g.
= (40 + 20) x 10 = 600 N.
and Distance or height = 80 x 25/100 = 20 m.
∴ Work done by her = 600 N x distance
∴ Total work done = 60 N x 20 m = 12000 J.
(iii) Useful work done = Load x g x distance covered
= 20 x 10 x 20 = 4000 J.
(iv) Power = Total work done/ Time
= 12000/25W = 480 W.
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