# Homework Help: Can someone please check this modified pendulum velocity problem

1. Dec 22, 2009

### yamugushi

[solved] Can someone please check this modified pendulum velocity problem

1. The problem statement, all variables and given/known data
I'm looking for the ballistic pendulum velocity for a simple machine (pull back lever, it shoots a marble into a block that raises to a certain degree measured)

I have the angle that the block is raised
length of the string
mass of block

2. Relevant equations
Ke=Pe (1/2MV^2=MGH)
cos@=length of sting - height/length of string

3. The attempt at a solution

.20cos25.3 = .20 - h

which gives me .02cm, which in turn gives me .6m/s, which seems a bit slow, I feel as if I'm messing up my trig but I don't know where...

I figured out I was using an incorrect derivation, I was just so fixed on thinking I had messed up my trig work

Last edited: Dec 22, 2009
2. Dec 22, 2009

### jegues

I'm confused in what you want us to check? What specific quantity are you concerned about?

The intial velocity of the object after its pulled back a certain distance?

3. Dec 22, 2009

### yamugushi

I've been given the manufacturers velocity, which is 5.5m/s, I'm getting less than 1m/s and honestly I don't see what I'm doing wrong.
BTW here is the pendulum I used:

4. Dec 22, 2009

### jegues

What exactly is this:

?

5. Dec 22, 2009

### yamugushi

Ke=Pe
1/2mv^2=mgh
masses cancel, divide both sides by .5
take the square root of both sides to get v=rad(GH)/.5

6. Dec 22, 2009

### denverdoc

Just your notation--rad is confused with radians. $$\sqrt{}$$ is available on the latex option on advanced setting with the icon:$$\Sigma$$ Or simply denote as sqrt(gh/.5)