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How to find the acceleration in an elevator using the increase in weight only (1.05x)

  • #1

Homework Statement


A person stands on a bathroom scale in a motionless elevator. When the elevator begins to move, the scale briefly reads 1.05 times the persons regular weight. Calculate the magnitude and direction of the acceleration of the elevator.

Homework Equations


F=ma

The Attempt at a Solution


Fg = 9.8m
ΣF = 9.8(1.05m + m)
0 = 1.05m + m
-m = 1.05m
-1 = 1.05

I know that's not true but I don't really know how to set up the problem
 

Answers and Replies

  • #2
haruspex
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ΣF = 9.8(1.05m + m)
Please explain your reasoning behind this equation.
What forces act on the person during the acceleration?
What acceleration results?
 
  • #3
Please explain your reasoning behind this equation.
What forces act on the person during the acceleration?
What acceleration results?
Actually the equation would be ΣF=9.8m-9.8(1.05m+m) according to my logic
but ΣF in this case is the difference between the force of gravity and the force of tension
the 9.8m part is to find the force of gravity on the person in the motionless elevator and the 9.8(1.05m+m) part is to find the force acting on the person when the elevator starts accelerating upward
to find ΣF you subtract the force of gravity from the fore of tension since it is larger
my physics teacher said that sometimes if you set up equations without numbers the variables will cancel out so I tried that and nothing cancels
The only number the problem gives me is 1.05 times the original weight when the elevator starts accelerating
and since the person is inside the elevator it's a system and the forces acting on the elevator vary directly with the forces acting on the person
 
  • #4
haruspex
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the 9.8(1.05m+m) part is to find the force acting on the person when the elevator starts accelerating upward
Maybe I misunderstand your notation, but that appears to reduce to 9.8(2.05)m. Is that what you meant?

nothing cancels
It will. When you have corrected your "9.8(1.05m+m)" and written it in simplest form, equate it to "ma", as in ΣF=ma.
 

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