Question

A man who weights 900N stands on a platform scale in a elevator. The elevator has a mass of 4000kg; the reading scale is 700N. What is the direction of the net force acting in the man

Answer 1

Hi there!

We know that there are TWO forces acting on the man.

• Force due to gravity: Acts DOWNWARD
• Normal force due to the elevator floor: UPWARD

We can express this in an equation. Let DOWN be NEGATIVE, and UP be POSITIVE.

`F_(net) = N - F_g`

Recall that a SCALE measures the NORMAL FORCE, NOT the WEIGHT. Therefore:

N = 700 N

W = 900 N

`F_(net) = 700 - 900 \\\\F_(net) = -200N`

Since downward is negative, the net force is acting DOWNWARD.