Kinematic Equation: Accel of Bullet Through 8.1cm Thick Board

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Homework Help Overview

The discussion revolves around a kinematic problem involving a bullet passing through a board. The bullet's initial and final velocities, as well as the thickness of the board, are provided, and participants are tasked with finding the average acceleration of the bullet. The subject area is kinematics.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the relevant variables for the kinematic equations, including initial and final velocities, distance, and the need for time. There are questions about how to incorporate the dimensions of the bullet and board into the calculations.

Discussion Status

Participants are actively exploring different kinematic equations and discussing the necessary variables. Some have suggested specific equations to use, while others are questioning the assumptions about time and displacement. There is no explicit consensus on the correct approach or answer yet.

Contextual Notes

There is uncertainty regarding the correct application of kinematic equations and the consistency of units. Participants are encouraged to list known variables and clarify their understanding of the problem setup.

krazykaci
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another one!

An indestructible bullet 1.86cm long is fired straight through a board that is 8.1cm thick. the bullet strikes the board with a speed of 452 m/s and emerges with a speed of 298 m/s. what is the average acceleration of the bullet through the board? answer in units of m/s^2

what would the length of the bullet and the width of the wall be used for in a kinematic equation? I know 452=v. and 298=v ... or is that wrong?
 
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Use the same formula for acceleration as your tennis ball question.
 
Think. You have to find the acceleration. List the things you know. Then look at your equations again. List all things that are relavant to kinematics.
 
what would the time variable be then?
 
If you don't know it label it as just t=?. But look at your equations, they all don't have something in it. Each one doesn't have one of these a,v,t,d so which oe should you use.
 
v=v.+a(t)

i know v=452m/s
v.=298 m/s
a= unknown
but i don't know what t should be, and it is known isn't it?
 
Do you need time?
Your missing a variable, distance.
There are other equations you can use.
 
oh, so I am using v^2=v.^2+2a(x-x.)? right?
 
Yes, List out everything you know before you even start a problem. This will help with some headaches. Look for what you don't know also and choose your equation with this information.
 
  • #10
so do I use 8.1 and 1.86 to find displacement?
 
  • #11
The bullet is only deaccelerated over 8.1cm. The width of the board.
 
  • #12
can you explain it in a different way. I don't understand how that fits into the equation.
 
  • #13
Your initial x=0 because the bullet has not been acted upon yet so your final x=8.1cm
 
  • #14
ok so the equation is 298^2=452^2+2a(8.1-0) right?
 
  • #15
looks good to me!
 
  • #16
the answer I am getting (-7129.63) is apparently incorrect. can you work it out and see if I am just doing my math wrong?
 
  • #17
whats the right answer?
 
  • #18
i don't know! i am doing the equation and I am getting that answer, but the computer is saying it is the wrong answer!
 
  • #19
well I'm getting a different answer than you also. Check your units. Stay consistent.
 

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