A physics student stands on a digital bathroom scale that is placed on the floor of…
PHYSICS · Multi-part · A Level · Physics · Mechanics and materials · Mechanics and materials
Problem
A 75kg physics student stands on a digital bathroom scale that is placed on the floor of an elevator. The scale displays the normal force it exerts on the student.
At t=0, the elevator begins moving downward from rest with a constant acceleration; at a later time, the elevator cable unexpectedly snaps and the elevator enters free fall.
(a) While the elevator is accelerating downward at 3.0ms−2, calculate the reading displayed by the scale.
(b) Determine the magnitude and direction of the elevator’s acceleration for which the scale would register a value of exactly 450N for the same student. Show all algebraic steps.
(c) Immediately after the cable snaps, what value (if any) will the scale display? Explain your answer in terms of forces acting on the student.
(d) Suppose a second identical scale is firmly bolted to the ceiling of the elevator and the student places her hands on it at the instant the cable snaps. Predict what, if anything, the upper scale would read during the free-fall interval, and justify your prediction.