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Force Elevator Problem!

by whoopie88
Tags: elevator, force
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whoopie88
#1
Oct13-10, 10:44 PM
P: 52
1. The problem statement, all variables and given/known data
Your mass is 65 kg. You stand on a bathroom scale in an elevator on Earth.

(a) What force would the scale exert when the elevator moves up at a constant speed?

(b) What force would the scale exert when it slows at 2.1 m/s2 while moving upward?

(c) What force would the scale exert when it speeds up at 2.1 m/s2 wile moving downward?

(d) What force would the scale exert when it moves downward at a constant speed?

(e) What force would the scale exert when it slows to a stop at a constant magnitude of acceleration?

2. Relevant equations
f=ma
fg=mg
fnet=mAnet
Ff=μῦFn


3. The attempt at a solution
I honestly have no idea what to do with all these Y forces going everywhere..Can someone walk me through the process of solving this problem?

THANK YOU IN ADVANCE FOR ANY HELP!!
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PhanthomJay
#2
Oct13-10, 10:54 PM
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Draw free body diagrams. There are 2 forces acting on the person, the person's weight, acting down, and the normal (scale) force acting up. Use Newton's laws F_net = ma when accelerating. At constant speeed or at rest, F_net =0 (no acceleration, per newton 1). Please show an attempt .
whoopie88
#3
Oct13-10, 11:09 PM
P: 52
I found (a), (c), and (d), but I can't find (b). Here is my attempt at solving it:

mAnet = -Fn + Fg
mAnet - Fg = -Fn
65(-2.1) - 65(9.81) = -Fn
774.15 = Fn

Help?

whoopie88
#4
Oct13-10, 11:09 PM
P: 52
Force Elevator Problem!

I also don't understand how to find (e)..
whoopie88
#5
Oct13-10, 11:28 PM
P: 52
Okay after working on this, I've solved it. Thanks anyways!


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