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Conservation/Conversion of energy

  • Thread starter drkidd22
  • Start date
59
0
1. Homework Statement
A mass of 4.5kg is dropped from a height of 3.3m above a spring. spring const is 25N/cm. How much is the spring compressed.


2. Homework Equations

F = 4.5*9.8 = 44.1

PE = mgh = 4.5*3.3*9.8 = 145.53

v = sqrt(2(9.8)(3.3)) = 8.04m/s

3. The Attempt at a Solution

The above are the few things I was able to grab out of the given information. The issue I'm having is plugging this into an equation to find the spring
 

Delphi51

Homework Helper
3,407
10
Energy is conserved in this problem. If you write
initial energy = final energy
and then fill in the details of the kinds of energy involved you will be able to solve for the spring compression.
 
59
0
so I get that mgh = 1/2mv^2+mgh?

145.53 = .5(4.5)(8.04)^2+(4.5)(9.8)h

.7m?

I don't think I did it right
 
59
0
Well I looked into a few of the formulas on the book and I get to a quadratic equation, but I'm still missing something here and I'm not sure what it is.

.5(.25)Y^2-(4.5)(9.8)Y+4.5(9.8)(-3.3)
0.125Y^2-44.1Y+145.53.

356? That's not possible so any adive on this will be appreciated.

Thnsx
 
59
0
Got it done. My equation above is right, the only problem was that I had to convert N/cm to N/m.

Thanks
 

Delphi51

Homework Helper
3,407
10
You didn't consider the spring!
Initially you have the mgh. When the mass hits the spring, it comes to a stop and you only have spring energy ½kx².
 

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