- #1
Vriska
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Homework Statement
The problem is to take a small ball of mass m on a uniform rod of mass m which is hung on a hinge vertically downward, they're asking to find the velocity to be imparted for it undergo a complete rotation.
I have the kinetic energy bit worked out but I'm getting the wrong answer equating it to potential energy
Homework Equations
Cm = x1m1+x2m2/(m1+m2)
The Attempt at a Solution
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Okay I'll assume the ball system nearly comes to a stop at the when it stands vertically. the cm of the rod will be l/2. this means that the mass is concentrated at l/2. now cm of the total system would be half way between the balland the cm of the rod. So it's l/2 + l/4 which is 3/4l. Mass = 2m so potential energy is lmg3/2.
.The books says this energy is 3mgl