Question

A man weighing 75 kg lift a body of 25 kg of height 10 m. In 5 min. Find the power

Answer 1

total workdone = force * diaplacement


force = mg
f = (25 + 75)*10
f = 1000N

and the displacement is 10m
so work done is 1000*10

= 10^4 j

so the power is
work / time

time = 5 min = 5 *60sec = 300seconds

power = 10^4/300
10/3
= 3.33watt.

Answer 2

Actually,
work done = f cos theta s
that means,
work done = force cos theta displacement
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cos theta is the angle between the surface and the force of attraction.
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if what is is being lifted up words making an angle of 90° to the surface.
then, the work done will be zero.
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In the above case,
the body of 25 kg is being lifted up words to a height of 10 m for 5 minutes.
Angle between the body and the surface = 90°
and we know that cos 90 = 0
so, Work done = Force × 0 × displacement
Work done = 0 joules
::::::::::::::::::::::::::::::::::::::::::::::::::
but, as we see this question by means of potential energy.
then, Potential energy = MGH
Potential energy = 25 × 10 × 10
Potential energy = 2500 joules

Power = energy consumed per second.
so, Power = 2500 / 5 × 60
Power = 8.333333333333333333 watts.
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