Ballistic pendulum change in kinetic energy problem

[victoriafello]

Homework Statement

a bullet of mass M is fired into a block of wood of mass m, the bullet sticks in the wood and causes it to swing upwards by height h

calculate the change in kinetic energy from the bullet to the bullet+wood

Homework Equations

kinetic energy = 1/2MV^2
V = SQRT (2gh)
Inital speed = m+M / m Sqrt(2gh)

so initial kinetic energy is 1/2 M m+M / m Sqrt(2gh)
final kinetic energy is 1/2 M + m SQRT (2GH)

The Attempt at a Solution

i know i need to divide final EK by initial EK but i am not sure if i have all the equations correct as when i try and do this i can't get to an answer

can anyone help>

 

[rl.bhat]

Since mass of the bullet is M, your expression for initial velocity is wrong. Check it.
They expect to find (initial KE - final KE)

 

[victoriafello]

Since mass of the bullet is M, your expression for initial velocity is wrong. Check it.
They expect to find (initial KE - final KE)

i have had another look and I am not sure if i should cancel the m's as they don't apply yet this would give me

Ini Vel = M SQRT(2gh)

is this better ?

 

[rl.bhat]

No.
Vi = (m+M)/M*sqrt(2gh)

 

[victoriafello]

ok then so where am i going wrong ? i have been thru my textbook and asked my teacher but i just can't get it right, i think the problem is with the formula for inital KE but however i go thru it i get the same result,

this needs to be in tomorrow so i am having a panic now

thanks