Maximum and Minimum Forces for Elevator Design

[Hotsuma]

Homework Statement

An elevator mass 4950 kg is to be designed so that the maximum acceleration is 6.10×10^-2g.

What is the maximum force the motor should exert on the supporting cable?

What is the minimum force the motor should exert on the supporting cable?

Homework Equations

\Sigma[\tex]F = ma<br /> <br /> <h2>The Attempt at a Solution</h2><br /> <br /> I know this should be so easy, but Mastering Physics is not liking my answers. I have tried multiplying the combined forces of acceleration and gravity multiplied over the mass to get a large force, that answer was incorrect. I noticed that the units of acceleration is in &#039;g&#039;, which caused me to believe they were referencing that amount multiplied by gravity instead of added to it, which resulted in another answer MP did not like. My results:<br /> <br /> F = 48800 N<br /> F = 2960 N<br /> <br /> Three significant figures, neither of those answers were correct (this is for F_max). I am afraid I am missing something really critical, and wanted to get another opinion. Maybe I&#039;m approaching this problem in the wrong way?

 

[Delphi51]

"combined forces of acceleration and gravity" sounds really good! But doesn't lead to the numbers you got. It would be interesting to see the details of your calculation.
F = ma + mg = ?

 

[Hotsuma]

Well mg + ma does equal 48800 N rounded to the number of significant figures the problem asks for.

The calculation I referred to is: 4950*(g+a), which equals 48900... Hmm...

Well, I only have one guess left, and I know that 48900 is not correct.

 

[Delphi51]

Ah, you are using a=0.061! It should be a = 0.061*9.81.

 

[Hotsuma]

So it should be calculated as such:

F = mga + mg = 51500N. Is this right?

 

[Hotsuma]

What about finding the minimum force?