How do I solve this Physics question please?

Question

A raindrop of mass 3.46  10^-5 kg falls vertically at constant speed under the influence of gravity and air resistance. Model the drop as a particle.

(a) As it falls 80 m, what is the work done on the raindrop by the gravitational force?

 ______ J

(b) What is the work done on the raindrop by air resistance?

 ______ J

Answer 1

A free body diagram would look like this:

We know that the force of gravity (F_g) is mass times the acceleration due to gravity (g) or 9.81 m/s²

F_g = mg

F_g = (3.46 x 10^-5)(9.81) = 3.39426 x 10^-4 N

Since the raindrop is falling at constant speed, there is no acceleration. That means the sum of the forces in the y-direction equals zero or that F_g = F_{Air Resistance}

a) Work = Fd So the work done by gravity is (3.39426 x 10^-4)(80) = 0.0272 Nm or, rounding to 1 sig fig, 0.03 Nm

b) The work done by the force of the air resistance is (-3.39426 x 10^-4)(80) = -0.0272 Nm or, rounding to 1 sig fig, -0.03 Nm. Notice it is negative because the travel is in the opposite direction to the force,