Solving Elevator Problem Homework Statement

[Anthonyphy2013]

Homework Statement

A woman stands on a scale in a moving elevator. Her mass is 50kg and the combined mass of the elevator accelerates upward. During the acceleration , the hoisting cable applies a force of 9350N. What does the scale read during the acceleration ?

Homework Equations

F net= T-MG= Ma
Apparent weight = mg(a/g+1)

The Attempt at a Solution

First we find a and the plug in the a in the apparent weight and we find the scale reading
first attempt: 9530-(50+815) = (815+50)a
and a= 1.22m/s^2
and the apparent weight = 9532N

 

[rude man]

Homework Statement

A woman stands on a scale in a moving elevator. Her mass is 50kg and the combined mass of the elevator accelerates upward. During the acceleration , the hoisting cable applies a force of 9350N. What does the scale read during the acceleration ?

Homework Equations

F net= T-MG= Ma
Apparent weight = mg(a/g+1)

The Attempt at a Solution

First we find a and the plug in the a in the apparent weight and we find the scale reading
first attempt: 9530-(50+815) = (815+50)a

You are mixing up Newtons with kg in this equation.
Your problem doesn't state it but I gather the mass of the elevator is 815 kg.

 

[mfb]

Where does the number 815 come from?
Please work with units, it is easier to spot errors that way. For example, you cannot subtract 50kg from 9350N, that does not make sense.

and the apparent weight = 9532N

It would be impossible to stand on a scale in that case (that is the weight of a car), the result cannot be true.

 

[Anthonyphy2013]

815 comes from the combined mass of the elevator and the scale .
9530N-(865*9.8)N=(865)a
a=1.22 m/s2
Apparent weight=N=Mg(a/g+1)
=(865*9.8)(1.22/9.8 + 1)
9532.3N
Is that corrected ?

 

[rude man]

815 comes from the combined mass of the elevator and the scale .

You mean 815 is the mass of the elevator, I think.

9530N-(865*9.8)N=(865)a
a=1.22 m/s2

That is finally correct.

Apparent weight=N=Mg(a/g+1)
=(865*9.8)(1.22/9.8 + 1)
9532.3N
Is that corrected ?

No. She's not going to weigh much more than at rest. And the scale reads in kg, not N.
So the answer is not much more than 50 kg.

 

[haruspex]

Apparent weight=N=Mg(a/g+1)
=(865*9.8)(1.22/9.8 + 1)

865? Isn't that going to give you the apparent weight of the elevator+passenger?

 

[Anthonyphy2013]

865? Isn't that going to give you the apparent weight of the elevator+passenger?

so you mean the mass is 50 not 865( 815+50) ?

 

[rude man]

so you mean the mass is 50 not 865( 815+50) ?

Yes. You're not measuring the weight of the elevator, right?