# Newtons third law, elevator question (free body diagram)

1. Apr 16, 2012

### supernova1203

1. The problem statement, all variables and given/known data

An elevator containing 3 passengers(with a mass of 72kg 84 kg and 35 kg) has a mass combined of 1030 kg . The cable attached to the elevator exherts an upward force of 12000 N. But the friction opposing the motion of the elevator is 1400 N.

a) Draw a free body diagram for all the forces acting on the elevator.

2. Relevant equations
Fg=mg

3. The attempt at a solution

Now since net force is greater for upward motion, we can assume the elevator is going up, since gravity + friction is still less than the upward force exherted, so elevator is going up,
but my question is...in the free body diagram..do i put both friction and force of gravity as a downward force???

Or should i just remove force of gravity and just put force of friction in the freebody diagram as a downward force?

The free body diagram i have in mind is in attachment, and thats what it looks like now....as always you dont need to download attachment to view it.

thanks!

#### Attached Files:

• ###### Fbd 1.jpg
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2. Apr 16, 2012

### PeterO

I believe you should be drawing both "gravity" and friction - down - but only Applied force up.

The net force is the vector sum of the three real forces - but I am not sure it is generally shown on these diagrams.

Also - you can do MUCH better with the arrows. The applied Force vector should be nearly 9 times as long as the friction Force.
How does the weight force compare in size?

3. Apr 16, 2012

### supernova1203

well this is not the actual diagram, its not to scale, the actual diagram is done in paper, i just sort of did a quick sloppy version to post here