# Newton's law, normal force, acceleration

1. Sep 29, 2011

### jehan4141

A 75 kg person is standing on a bathroom scale in an elevator. The scale is calibrated to read in Newtons. The elevator is accelerating upward at 135 m/s2. What is the reading on the scale? What apparent value of g does the man give?

The Free Body Diagram
Normal on the man, upward
Weight mg of the man, downward

My Attempt/Logic
The only two forces acting on the man are normal force and weight.

FN - mg = ma
fN = mg + ma, where N is the reading on the scale.

FN = (75)(9.8) + (75)(135)
FN = 10860 N

The solution reads 8.5x102 N? Am I doing something wrong? This problem seems very basic, but I am obviously missing something.

2. Sep 29, 2011

### Staff: Mentor

Are you sure the acceleration wasn't 1.35 m/s^2. 135 m/s^2 is not very realistic.

3. Sep 29, 2011

### jehan4141

4. Sep 29, 2011

### jehan4141

It is much closer with 1.35 m/s2, However it is still a little off??? I am not sure if there is even anything wrong with the way I am doing it :( it seems correct?

5. Sep 29, 2011

### Staff: Mentor

If you take g = 10 m/s^2 it's pretty close. (But it definitely says 135 m/s^2.)