Concept:A falling body reaches terminal velocity when the net force acting on it becomes zero.
Explanation:Consider a metal ball moving down through glycerine.
Three forces act on it:
Weight
W acting downward.
Upthrust
U acting upward.
Viscous force
V acting upward, opposing the motion.
At terminal velocity, the ball is no longer accelerating.
Therefore, the downward force must be exactly balanced by the sum of the upward forces.
This gives:
W=U+VSo, the condition for terminal velocity is that the weight
W equals the sum of the upthrust
U and the viscous force
V.
Answer:Option B:
W=U+V