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January 30, 2015

January 30, 2015

Posted by **Em** on Saturday, February 19, 2011 at 4:22pm.

- Physics -
**drwls**, Saturday, February 19, 2011 at 4:32pmThe easy way to do this is with conservation of energy, since you have to deal with an increasing acceleration rate, which would make the equation of motion rather messy. You can use energy conservation because it is frictionless.

When it starts out, the center of mass of the chain is (1/2)*(L/4) = L/8 below the table surface.

When 1/4 of the chain's length remains ion the table, the center of mass is

(1/2)(3L/4) = 3L/8 below the table surface. The change in CM height is L/4. At that time, the velocity V is given by

M g L/4 = (1/2) M V^2

g L = 2 V^2

V = sqrt(gL/2) = 2.96 m/s

- Physics -
**bobpursley**, Saturday, February 19, 2011 at 4:46pmLEt total mass be m

force pulling: masshanging over *g

force puling: mg*x/1.79 where x is the amount hanging over.

well, then force pulling is linear with the length hanging over, so the average force between .25x and .75 x is at .5x

or avg force= mg/2

Vf^2=Vi^2+2ad

Vf^2=0+2(avgforce/m)(1/2 1.79)

Vf= sqrt (g*1.79/2)

check my thinking.

Vf= sqrt (2*

- Physics -
**bobpursley**, Saturday, February 19, 2011 at 4:47pmignore the last line,old typo. I agree with drwls, it is the same argument.

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