A 90-kg man stands in an elevator that is moving up at a constant speed of 5.0 m/s.The force exerted by him on the floor is about:
A)0 N
B)90 N
C)880 N
D)450 N
E)49 N

Question

Quizplus · Accepted Answer

Since the elevator is moving at a constant speed, the net force acting on the man is zero (Newton's first law). Therefore, the only forces acting on him are gravity (downward) and the normal force from the elevator floor (upward). The force due to gravity is $mg$, where $m = 90\, \text{kg}$ and $g \approx 9.8\, \text{m/s}^2$, giving a force of $90 \times 9.8 = 882\, \text{N}$. The closest answer to this calculation is 880 N, indicating that the force exerted by the man on the floor is essentially equal to his weight, as expected when there is no acceleration.

A 90-Kg Man Stands in an Elevator That Is Moving