- #1
kingsmaug
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Homework Statement
A piece of putty of mass m = 0.75 kg and velocity v = 2.5 m/s moves on a horizontal frictionless surface. It collides with and sticks to a rod of mass M = 2 kg and length L = 0.9 m which pivots about a fixed vertical axis at the opposite end of the rod as shown. What fraction of the initial kinetic energy of the putty is lost in this collision?
Homework Equations
KE = 1/2mv^2
KE = 1/2Iw^2
L=mvr
L=Iw
I=mL^2/3
I=mr^2
r=L (I'm using the pivot as the point of origin)
The Attempt at a Solution
Based on the wording, it's an inelastic collision, and the putty sticks to the rod.
So, momentum is conserved:
mvL = (mL^2/3+mL^2)w
Using numbers, I found that w = 1.176 rad/s
The initial KE is 1/2mv^2= 2.34
The final KE is 1/2Iw^2= 0.79
KElost/KEi=(KEi-KEf)/KEi = 0.66
but the answer is wrong.