- #1

Thefox14

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## Homework Statement

[PLAIN]https://wug-s.physics.uiuc.edu/cgi/courses/shell/common/showme.pl?cc/DuPage/phys2111/fall/homework/Ch-08-GPE-ME/twomasses_vertical_spring/3.gif

A block of mass 7 kg hangs on a spring. When a second block with an identical mass of 7 kg is tied to the first, the spring stretches an additional ho = 1.3 m.

a) What is the value of the spring constant k?

Now the string is burned and the second block falls off.

b) How far above its original position does the remaining block attain its maximum speed?

c) What is the maximum speed attained by the remaining block?

## Homework Equations

[tex]W_{Total} = \Delta K[/tex]

[tex]W_{NC} = \Delta ME[/tex]

## The Attempt at a Solution

I was able to figure out part a and b fairly easily.

A) was 52.82 N/m

B) was 1.3 m

Part c is where I'm stuck. So far what I've done is set the point where the string is at equilibrium with no weight on it where potential energy = 0. Since there are no Non Conservative forces I sad:

[tex]\frac{1}{2}k(2h)^{2} - mg(2h) = \frac{1}{2}mv_{f}^{2}[/tex]

Where 2h is twice the answer found in B

I get the left side to be a negative number, what am i doing wrong?

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