- #1
MMVS
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Homework Statement
Elevator initially at rest.
Equilibrium length L0=40.0cm
60-kg person stands on spring
L1= 32.0cm
The elevator than speeds upwards at 2.50 m/s2
What is the new length (L2)
Homework Equations
Fnet=ma
Fsp=-kdeltaX
FG=mg
The Attempt at a Solution
Taking down as positive y hat direction
Before:
Fnet=Fsp+FG
0=-k(0.32-0.40)+(60.0)(9.81)
K=-7358
After:
Fnet=Fsp+FG
ma=-kdeltaX+mg
m(-2.5)=-(-7358)(L2-0.40)+60(9.81)
L2=[{60(-2.5)-60(9.81)}/-(-7358)]+0.40
=0.30m from equilibrium
I am confused since i don't know how this makes sense according to the coordinate system. (I know the answer is right as my prof posted the answer, not the work, just answer)
At rest change in x = -0.08
When accelerating change in x= -0.10
But since my coordinate system is set up so Y-hat is positive is the downward direction doesn't this mean my spring is being displaces upward?
This doesn't make sense to me , can someone please explain very clearly?