# Homework Help: Elevator problem help

1. Nov 19, 2005

### Sar06

A person stands on a bathroom scale in a motionless elevator. When the elevator begins to move, the scale briefly reads only 0.72 of the person's regular weight. Calculate the acceleration of the elevator, and find the direction of acceleration.
I know that the direction of acceleration is downward, but I'm not quite sure how to calculate it. I know that F=ma...
It would be much appreciated if someone could point me in the right direction.
Thanks
-SAR

2. Nov 19, 2005

### lightgrav

no, F is not equal to ma ... the SUM of all Forces is equal to ma .

The Earth pulls down on the person, and the scale surface pushes up on them.

3. Nov 19, 2005

### James R

The scale reads the force exerted on it, which is equal to the upwards force it exerts on the person standing on it. That person has two forces on them: the force of the scale pushing upwards, and the force of gravity pulling downwards. The net force on the person is the vector sum of these two forces.

So, here are the questions:

1. What is the force of gravity on the person?
2. What is the force provided by the scale?
3. What is the net force on the person?
4. How is the net force related to the person's acceleration?
5. What is the person's acceleration?