A woman stands on a bathroom scale in a motionless elevator. When the elevator b

Question

A woman stands on a bathroom scale in a motionless elevator. When the elevator begins to move, the scale briefly reads only 0.75 of her regular weight. Calculate the acceleration of the elevator, and find the direction of acceleration. (a) If and in Fig. 4-53, determine the acceleration of each block. (b) If initially is at rest 1.250 m from the edge of the table, how long does it take to reach the edge of the table if the system is allowed to move freely? (c) If how large must be if the acceleration of the system is to be kept at 1/100g

Explanation / Answer

The scale is reading the Normal force. Using the equation we found for elevators moving down:

Ndown = mg - ma = w1=0.75w

At rest, the Normal force was

NREST = mg = w

Divide one equation into the other to find a ratio.
Ndown/Nrest = m(g-a)/mg

0.75w/w= (g-a)/g

0.75 =1- (a/g)

a/g=0.25

a= 9.8 * 025

a= 2.45m/s2

Since the acceleration is positive the direction is up.

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