Can't Figure out what I am doing wrong F=MA (easy problem)

[lanzjohn]

Homework Statement

An elevator (mass 1020kg) is to be designed so that the maximum acceleration is 0.062 g. What is the maximum force the motor should exert on the supporting cable?

Homework Equations

F=MA

The Attempt at a Solution

(.062)(9.8 m/s^2) = .6076 m/s^2

F = (1020)(.6076)

F = 619.752 N

Why is that wrong?! Unless g means something else I don't understand what's up?

Thanks for your time.

 

[ehild]

The elevator accelerates upward. What force(s) act on it? Is it only the force of the motor?

ehild

 

[BruceW]

You've missed out the force on the elevator due to gravity.
F=mg+ma
gives the required force 'F' that the motor must exert to accelerate upwards at acceleration 'a'

 

[lanzjohn]

Well there is the force of gravity. But isn't that already incorporated into the acceleration of the motor?

I guess there is the Force of tension as well...

 

[lanzjohn]

Ohh I gotcha. I guess I assumed the tension of the rope canceled out the force of gravity... So it just left the acceleration or Force rather due to the motor. We are just starting to learn dynamics so I am a little shaky on some concepts... Got to love summer classes- they move so damn fast.

 

[BruceW]

Sorry, I realize I just gave an answer without helping lanzjohn to figure it out on his own.
But I think he just forgot, since I did that a lot when I was first doing these types of questions.