Question : A student stands on a bathroom scale in an elevator at rest on the 64th floor of a building. The scale reads 8
As the elevator moves up, the scale reading increases to 935 N, then decreases back to 828 N. Find the acceleration of the elevator.

As the elevator approaches the 74th floor, the scale reading drops to 782 N. What is the acceleration of the elevator?
floor scale

Best answer:

Answer by M&M
Well, F=ma
since at rest, the acceleration is 9.8m/s^2 (some ppl just round to 10), you can find the mass, which would be 84.49 (if you used 9.8) or 82.8 (if you used 10)
Now that you know the mass, you can use it at different forces to determine the acceleration.
So in the first one, the new force is 935. the mass is still the same, so use F = ma again to determine the a, which would be 11.3 if you use a mass of 82.8 or 11.1 if you used 84.5.
BUT!!! you have to take in account the acceleration of gravity on the force put against the scale. So you subtract gravity away, and the acceleration is only 1.3 (regardless of which gravity and weight you used as long as you matched them)

For the second one, it’s the same but the opposite. the difference in force is the difference in acceleration.