(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

When the elevator is at rest, the scale reads W.

Suppose the elevator now accelerates down-ward at a constant rate of 0.4 g.

What is the ratio of the new scale reading to the value W of the scale reading when the

elevator is at rest?

2. Relevant equations

Force equations:

F = ma

Fnet = 0

3. The attempt at a solution

What I did is to draw a force diagram that resulted:

At rest:

Fn - mg = 0

mg = Fn

Accelerating:

Fn - mg = -ma, where a = .4g

mg = Fn + .4mg

I set Fn = mg = 1, so ratio becomes to 1.4 -> (1 + .4)/(1)

The real answer is .6, but I'm not really sure how to get that. I know if I do:

Fn - mg = ma

mg = Fn - .4mg, the ratio then becomes to .6

Why is it "ma" instead of "-ma" when the elevator is accelerating downwards?

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# Homework Help: Elevator at rest compared to when its accelerating

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