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**1. Homework Statement**

A person stands on a bathroom scale in a motionless elevator. When the elevator begins to move, the scale briefly reads

only 0.78 of the person’s regular weight.

a. Calculate the acceleration of the elevator.

b. Find the direction of acceleration.

**2. Homework Equations**

Sum of forces.

**3. The Attempt at a Solution**

I know the equation is F_normal-mg=ma but don't understand how it was derived.