Concept:Weightlessness in a descending lift occurs when the lift's downward acceleration equals the acceleration due to gravity.
Explanation:When a lift descends with acceleration
a, the apparent weight is the normal reaction
R.
The net force equation is:
mg−R=ma.
Therefore,
R=m(g−a).
The man feels weightless when
R=0.
This happens when
m(g−a)=0, which gives
a=g.
Thus, the lift must accelerate downward at the same rate as gravity.
In this condition, both the man and the lift fall together, so no reaction force acts on him.
Answer:C. the lift's acceleration is same as acceleration due to gravity.