Question

A 700 man stands in a scale on the floor of an elevetor.the scale records the force it exerts in whatever is on it.what is the scale reading if the elevetor has an acceleration of (a) 1.8m/s up? (b)1.8m/s down?

Answer 1

a. 829 N
b. 571 N

Explanation:

I will assume the man weighs 700 N and the 2 accelerations are `1.8 m/s^2` up and down. If the elevator were stationary, the scale would be applying an upward force of 700 N to hold the man in equilibrium.

a. When accelerating upwards, the scale must apply an extra upward force. For the next bit, I will need the man's mass, m.

`m = "weight"/g = (700 N)/(9.8 m/s^2) = 71.4 kg`

So, the extra upward force to accelerate the man upwards is given by

`F = 71.4 kg*1.8 m/s^2 = 129 N`

The scale reading is a measurement of the upward force the scale is providing for whoever is standing there. When accelerating the man upwards, the total upward force is
`700 N+129 N = 829 N`.

b. When the acceleration is downward, the 129 N would be subtracted from the 700 N.
`700 N-129 N = 571 N`

I hope this helps,
Steve