Ball drops onto rod on a fulcrum and launches another ball into the air

[graustet]

Homework Statement

A 4.80 -kg ball is dropped from a height of 10.5 m above one end of a uniform bar that pivots at its center. The bar has mass 8.00 kg and is 4.00 m in length. At the other end of the bar sits another 5.10 -kg ball, unattached to the bar. The dropped ball sticks to the bar after the collision.

how high will the other ball go after the collision??

Homework Equations

Im assuming a change in kinetic/potential energy, moment of inertia, conservation of momentum

The Attempt at a Solution

i found the potential energy of the first ball and used that to find the speed of the ball before it hits the rod. using the conservation of momentum of a inelastic equation i found the resulting speed of the rod and first ball. using that speed i applied it to the rod and other ball to find its kinetic energy. then i set the kinetic energy equal to the potential to find the height. i got like 10.3 meters. i know that's not the answer because by reasoning i thin kt hat the answer should be around 1 meter or so.

 

[tiny-tim]

welcome to pf!

hi graustet! welcome to pf!

… i found the potential energy of the first ball and used that to find the speed of the ball before it hits the rod. using the conservation of momentum …

nooo … this is a turny thingy …

try conservation of angular momentum

(add in future, please show your calculations)