Bullet & Pendulum Homework: Determine Horiz. Displacement

[BMWPower06]

Homework Statement

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.

Homework Equations

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

The Attempt at a Solution

Im stuck and don't know what else to do

 

[malawi_glenn]

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]

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]

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]

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?