A mass of mass m, experiences a viscous drag, F and an upthrust, U as he descends towards the ground at a steady velocity, Using a parachute. If the acceleration of free fall is g, which of the following expressions is correct?
A
FU = mg
B
U + F - mg = 0
C
U - F = mg
D
F - U - mg = 0
Verified Correct Answer: B.
Physical Principles & Numerical Solution
The forces acting on the mass include:
Weight: W = mg (downward)
Upthrust: U (upward)
Viscous Drag: F (upward)
Since the mass is descending at a steady velocity, the net force acting on it is zero. This means that the upward forces (upthrust and viscous drag) balance the downward force (weight): mg = U + F = U + F - mg = 0
Source: Myschool Past Questions Archive (Record #34825)