A 2.5-kg object falls vertically downward in a viscous medium at a constant speed of 2.5 m/s. How much work is done by the force the viscous medium exerts on the object as it falls 80 cm?
A) +2.0 J
B) +20 J
C) −2.0 J
D) −20 J
E) +40 J

Question

Quizplus · Accepted Answer

The object falls at a constant speed, meaning the net force is zero. The gravitational force is balanced by the viscous force. The work done by the viscous force is equal in magnitude and opposite in sign to the work done by gravity. Work done by gravity is mgh = 2.5 kg * 9.8 m/s² * 0.8 m = 19.6 J, rounded to 20 J. Thus, the work done by the viscous force is -20 J.

A 25-Kg Object Falls Vertically Downward in a Viscous Medium at at a Constant