The rain drop of mass 1 g, starts with zero velocity from a height of 1 km. It hits the ground with a speed of 5 m/s. The work done by the unknown resistive force is _______ J.
(take g = 10 m/s$$^2$$)

Use work-energy theorem:

$$W_{gravity}+W_{resistive}=\Delta K$$

given:

$$m=1g=10^{-3}kg$$

h=1 km=1000 m

u=0,v=5 m/s

step 1: work done by gravity

$$W_g=mgh=10^{-3}\times10\times1000=10J$$

step 2: change in kinetic energy

$$ΔK=\frac{1}{2}mv^2=\frac{1}{2}\times10^{-3}\times25=0.0125J$$

step 3: resistive work

$$10+W_r=0.0125$$

$$W_r=0.0125-10=-9.9875J$$

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The rain drop of mass 1 g, starts with zero velocity from a height of 1 km. It hits the ground with a speed of 5 m/s. The work done by the unknown resistive force is _______ J.(take g = 10 m/s$$^2$$)