Physics
posted by Mary .
A bullet mass 10 g strikes a log with a mass of 25 g suspended from a 3 meter long string. The bullet lodges in the log which swings up through an angle of 30 degrees. Find the speed of the bullet just before it hit the log.

The law of conservation of linear momentum
m•v = (m +M) •u.
v =(m +M) •u/m.
The law of conservation of energy
KE =PE,
(m+M) •u^2/2 =(m+M) • g•h,
u = sqrt (2•g•h).
Since h =L(1cosα) ,
v =[(m +M) /m] • sqrt[2•g•L(1cosα)].