What was the speed of the bullet before it hit the block?

[PhysicsGirl]

Physics HELP!

Homework Statement

A 2.00-g bullet hits and becomes embedded in a 5.00-kg wood block which is hanging from a 1.40-m long string. This causes the block to swing through an arc of 4.50. What was the speed of the bullet before it hit the block?

Homework Equations

The Attempt at a Solution

I tried to set the masses equal to each other and then use cos for 4.50 in an attempt to find v not

 

[berkeman]

You need to show some of your work before we can offer tutorial help -- that's in the PF Rules.

What are two approaches that you could take to this problem? Why is the conservation of total energy approach the easiest?