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Question
A rain drop of mass 1 g falling from a height of 1 km hits the ground with a speed of 50 m/s. If a resistive force acts on the drop, then the work done by the resistive force is (Take g:10 m/s2)
A rain drop of mass 1 g falling from a height of 1 km hits the ground with a speed of 50 m/s. If a resistive force acts on the drop, then the work done by the resistive force is (Take g:10 m/s2)
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Solution
The correct option is D −8.75 J
Given:
m=1 g=10−3 kg
h=1 Km=1000 m=103 m
The change in kinetic energy of the drop is
ΔK=12mv2−0 (∵u=0)
= 12×10−3×50×50=1.25 J
The work done by the gravitational force is
Wg=mgh=10−3×10×103=10 J
According to work-energy theorem,
ΔK=Wg+Wr
Where Wr is the work done by the resistive force on the rain drop
Wr=ΔK−Wg=1.25 J−10 J=−8.75 J
Given:
m=1 g=10−3 kg
h=1 Km=1000 m=103 m
The change in kinetic energy of the drop is
ΔK=12mv2−0 (∵u=0)
= 12×10−3×50×50=1.25 J
The work done by the gravitational force is
Wg=mgh=10−3×10×103=10 J
According to work-energy theorem,
ΔK=Wg+Wr
Where Wr is the work done by the resistive force on the rain drop
Wr=ΔK−Wg=1.25 J−10 J=−8.75 J
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