# Bullet and Pendulum

#### BMWPower06

1. The problem statement, all variables and given/known data
An 16.2 g rifle bullet traveling 240 m/s buries itself in a 3.54 kg pendulum hanging on a 2.90 m long string, which makes the pendulum swing upward in an arc. Determine the horizontal component of the pendulum's displacement.

2. Relevant equations

I used the Y center of mass equation which is:
Ycm= m1y1+m2y2/m1+m2 but i got 2.9

3. The attempt at a solution
Im stuck and dont know what else to do

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#### malawi_glenn

Homework Helper
use conservation of (total) energy and momentum. Neglect the heat that the bullet will "create" when hitting the pendelum. You must use some trigometry also.

#### Doc Al

Mentor
Consider the interaction as having two stages:
(1) The collision of bullet and pendulum--what's conserved?
(2) The rise of the pendulum+bullet (post collision)--what's conserved?

#### BMWPower06

Consider the interaction as having two stages:
(1) The collision of bullet and pendulum--what's conserved?
(2) The rise of the pendulum+bullet (post collision)--what's conserved?
so i find the PE+KE=PE+KE for both parts

or in other words

.5MV2=mgh for both parts?

#### malawi_glenn

Homework Helper
Yes.

First the energy is the kinetic energy of bullet. Then all energy will be potential energy of the pendelum and the bullet. (m1+m2)gh

#### Doc Al

Mentor
so i find the PE+KE=PE+KE for both parts

or in other words

.5MV2=mgh for both parts?
Not exactly. Different quantities are conserved in each part of the motion. For example: During the collision, mechanical energy is not conserved. What is?

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