A person with mass of 55 kg is standing on a scale in an elevator. The elevator is moving up and accelerating at 1.5 m/s^2 for 3 seconds, then continues with constant speed. Find the scale reading a) before starting to move, b) when accelerating, c) when
moving at constant speed?

## Find the scale reading?

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# 1 Answer

Sum of the forces in the vertical direction F

_{y}= F_{N }+ (-mg) = ma(a) At rest, ma= 0.

Scale reading is equal to F

_{N }and is equal to (mg)F

_{N}= 55kg *(9.8m/s) = 539 N = 121 lbs(b) at a=1.5m/s

^{2},F

_{N }= mg + ma = (55kg)(9.8m/s^{2})^{ }+ (55kg)(1.5m/s^{2})^{ }= 621.5 N = 140 lbs(c) at constant speed, a = 0,

same as (a) scale reading is equal to F

_{N}= 539 N = 121 lbs