A coolie of mass 55 kg move a load of 25 kg on his head upto 50 stairs, each of height 20 cm in 50 s. If g is 10 m/s², then find

(a) gravitational force acting on coolie,

(b) work done by him

(c) his power in watt

(d) the gravitational force is increased by two times, then calculate the power.

Given,

Mass (m_c) = 55 kg

Load = 25 kg

Total load

50 stairs of height 20 cm,

so distance = 50 x 20 = 1000 cm

Converting cm into m

100 cm = 1m

so, 1000 cm = $\dfrac{1000}{100}$ = 10 m

Time = 50 s

(a) Gravitational force (F) = (m_c + load) x g

Substituting the values in the formula above we get,

F = (55 + 25) x 10 = 800 N

Hence, gravitational force acting on coolie = 800 N

(b) F = 800 N

distance (S) = 10 m

work done = ?

work done = F x S = (m_c + load) x g x S

Substituting the values in the formula above we get,

W = (55 + 25) x 10 x 10 = 8000 J

(c) work done (W) = 8000 J

time taken (t) = 50

Power = $\dfrac{\text{work done}}{\text{time taken}}$

Substituting the values in the formula above we get,

Power = $\dfrac{8000}{50}$ = 160 W

Hence, power in watt = 160 W

(d) If gravitational force is increased two times i.e., F = 2 x 800 = 1600 N

Substituting the values in the formula above we get,

W = 1600 x 10 = 16000 J

Power = $\dfrac{16000}{50}$ = 320 W

Hence, power in watt = 320 W