Question

A man stands on a scale while riding an elevator. The mass of the man is 84kg. What is the elevator's acceleration if the scale reads 1025 Newtons?

Answer 1

I found `2.4m/s^2`

Explanation:

The reading of `1025N` represents the Normal Reaction of the surface of the scale:

If the elevator is at rest then the reading of the scale would be exactly the weight `vecW` of the man, equal to: `mg=84*9.81=824N`.
But here we have a situation of acceleration or non-equilibrium between the two forces and so the normal reaction has to be different.
If we cut the cable of the elevator the reaction would disappear and the acceleration (downwards) would be exactly `vecg`.