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?
Sum of the forces in the vertical direction Fy = FN + (-mg) = ma
(a) At rest, ma= 0.
Scale reading is equal to FN and is equal to (mg)
FN = 55kg *(9.8m/s) = 539 N = 121 lbs
(b) at a=1.5m/s2,
FN = mg + ma = (55kg)(9.8m/s2) + (55kg)(1.5m/s2) = 621.5 N = 140 lbs
(c) at constant speed, a = 0,
same as (a) scale reading is equal to FN = 539 N = 121 lbs