A raindrop of mass 1 g starts from rest at a height of 1 km.
It reaches the ground with a speed of 5 m/s.
Find the work done by the unknown resistive force.
Take:
g = 10 m/s²
Mass:
m = 1 g = 10−3 kg
Height:
h = 1000 m
Initial kinetic energy:
Ki = 0
Final kinetic energy:
Kf = ½mv²
= ½ × 10−3 × 25
= 0.0125 J
Loss in potential energy:
mgh
= 10−3 × 10 × 1000
= 10 J
Using work-energy theorem:
Wgravity + Wresistive = ΔK
10 + W = 0.0125
W = −9.9875 J
The negative sign shows that the resistive force opposes the motion.
Final Answer
−9.9875 J