The force of air resistance on a raindrop is 4×10−5 N when it falls with a terminal velocity of 4.7 m/s. The acceleration of gravity is 9.8 m/s2. What is the mass of the raindrop? Answer in units of kg.
The terminal velocity of the raindrop is the velocity at which the force of air resistance is equal to the weight of the raindrop (or the force of gravity which is the same). Therefore, we can write: F_resistance=mg. From this formula we can find the mass of the raindrop: m=F_resistance/g=(4∙〖10〗^(-5) N )/(9.8 m/s^2 )=4.1∙〖10〗^(-6) kg.