A long light cord of length 
hangs a log of mass 
(ballistic pendulum). In the horizontal direction, a ball hits the log at a speed of 
and bounces off the log at a speed of 
. After an elastic collision of the ball with the log, the cord with the log deviates from the vertical by an angle 
.
How high does the log rise after the collision?
What is the speed of the log immediately after the collision?
What is the mass of the ball?
Figure 1: Ballistic pendulum.
Note: A ballistic pendulum is a thread (mathematical) pendulum, hanging on long strings, so that its oscillation time is large; it is used to measure the momentum.
