Weight of a person in a elevator going down

stealthcataf

Im new to physics and im trying to do some problems here, I hope someone can help me, here it goes :

If a passenger with a mass of 72.2kg stands on a weight scale in a elevator. What is the reading on the scale if the elevator goes down with a constant acceleration of 3.20 m/s^2.

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whozum

If the elevator was descending at constant acceleration of 9.8m/s^2, what would the scale read? Why?

What does this tell you about the effective acceleration on the passenger?

stealthcataf

Ive done some calcs, correct me if im wrong

m=72.2kg
a=-3.20 m/s^2

SumFx=0
SumFy=Fn-mg=ma

ma=72.2(-3.20)=-231.04n

Fn=mg+ma=72.2(-9.8)+72.2(-3.20)=-938.6n
Is this the apparent weight?

whozum

If the elevator is going down, then is he pressing MORE on the scale or less?
It is the normal force that gives the reading on the scale. How is the normal force affected when the elevator is falling?

gunblaze

Weight of person=72.2*9.81=708.282
upward lift on person=72.2*3.2=231.04
Therefore net 'weight' of person=708.282-231.04=477.242

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