Ballistic Pendulum Rifle: Solving for Post-Collision Height

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Homework Help Overview

The problem involves a ballistic pendulum scenario where a bullet collides with a pendulum, and the goal is to determine how high the combined system rises after the collision. The subject area includes concepts of momentum, kinetic energy, and potential energy in the context of mechanics.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the conservation of energy and the relationship between kinetic and potential energy. There are inquiries about the formulas for kinetic energy and potential energy, as well as the setup of the problem. Some participants express uncertainty about how to apply the bullet's velocity and the masses involved in the collision.

Discussion Status

The discussion is ongoing, with participants sharing hints and guidance regarding the stages of the problem. There is recognition that the collision does not conserve energy, but other principles may apply. Multiple interpretations of the problem setup are being explored, and participants are seeking clarification on specific concepts.

Contextual Notes

Participants are navigating the complexities of the problem, including the distinction between the masses before and after the collision. There is a noted lack of consensus on how to proceed with the calculations, and some participants are still grappling with the fundamental principles involved.

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The problem:

https://tycho-s.phys.washington.edu/cgi/courses/shell/common/showme.pl?courses/phys121/autumn08/homework/06/IE_algebra_ballistic_pendulum_MOM/pic.gif

A rifle bullet of mass m = 0.03 kg traveling at vb = 240 m/s collides with and embeds itself in a pendulum of mass M = 2.88 kg, initially at rest and suspended vertically by massless strings of length L = 2 m.

How high does the pendulum-bullet combination rise after the collision?

I don't know the process for solving this equation, so help would be appreciated.
 
Last edited by a moderator:
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Energy preservation. Kinetic gets converted into potential.
 
Okay, so I need to use PE = mgh. I don't understand what I do with the velocity of the bullet and how to setup the problem, if I could get a little more guidance it would help me out

Thanks.
 
What is formula for kinetic energy?
 
We did this the other day, except we just manipulated the formulas instead of working with actual values.
I am going to attempt to make sense of what I have for that note, so you may hear from me soon...
 
Borek said:
What is formula for kinetic energy?

KE = (1/2)mv2
 
Is there something you still don't know? Just beware which mass is which - ballistic pendulum mass after hit is that of pendulum PLUS bullet.
 
Borek said:
Is there something you still don't know? Just beware which mass is which - ballistic pendulum mass after hit is that of pendulum PLUS bullet.

I don't understand what it is I do with the equation for Kinetic Energy, I'm supposed to find the height of the bullet-pendulum system after the bullet hits the pendulum.
 
h as of mgh.
 
  • #10
This problem is best solved in two stages:
(1) The collision itself. You need to find the speed of the block+bullet immediately after the collision. Hint: Energy is not conserved, but something else is.
(2) The rising of the pendulum after the collision. Here you do use energy conservation, as Borek explains.
 
  • #11
Doc Al said:
Hint: Energy is not conserved, but something else is.

Do we have an emoticon for selffishslapping? :blushing:
 

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