Projectile Motion of rifle bullet

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Homework Help Overview

The problem involves projectile motion, specifically analyzing the flight of a rifle bullet aimed horizontally at a target 44m away, which impacts 3.0 cm below the aim point. The participants are tasked with determining the bullet's flight time and speed as it leaves the barrel.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the relationship between vertical displacement and flight time, questioning how to find the bullet's velocity without an angle. Some explore the need for equations related to vertical motion and acceleration.

Discussion Status

The discussion has seen various attempts to clarify the relationship between flight time and velocity. Some participants have provided equations and insights into vertical displacement, while others have expressed confusion about the necessary calculations. A participant reports successfully determining flight time and velocity, indicating some progress in understanding the problem.

Contextual Notes

There appears to be some confusion regarding the use of equations for projectile motion, particularly in distinguishing between horizontal and vertical components. The lack of an angle is noted as a point of concern in the initial discussions.

aligass2004
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Homework Statement


A rifle is aimed horizontally at a target 44m away. The bullet hits the target 3.0 cm below the aim point. a.) What was the bullet's flight time? b.) What was the bullet's speed as it left the barrel?


Homework Equations


Xf = Xi +Vixt + 1/2(a)(t^2)
Vfx = Vix + at
Vfx^2 = Vix^2 + 2ax(t)


The Attempt at a Solution


I have tried figuring this out. I know that the velocity needs to be found, and I know that the velocity then needs to broken into components. I'm just having problems without an angle given.
 
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The vertical displacement is 0.03m. You can use that to get the flight time. The bullet is shot horizontally. hence the angle is 0.
 
Ok, but how do you find the velocity?
 
aligass2004 said:
Ok, but how do you find the velocity?

Did you find the flight time?
 
Don't I need the velocity to find the flight time?
 
aligass2004 said:
Don't I need the velocity to find the flight time?

No you don't. You need the flight time to find the velocity. :wink:

What is the vertical displacement? write an equation for vertical displacement in terms of time.
 
Ok, you said the vertical displacement is .03m. So is the equation delta x = Vx(delta time)?
 
aligass2004 said:
Ok, you said the vertical displacement is .03m. So is the equation delta x = Vx(delta time)?

no. that equation won't work. it's accelerating vertically... So you need an equation for accelerated motion.
 
I finally figured it out. I used Yf = Yi + Vyi(t) + 1/2ay(t^2). Since the angle is zero because it's shot horizontally, the y component of velocity is zero, eliminating the middle term. So I just plugged in and got the time to be .078s. Then I used Xf = Xi + Vx(t). I found Vx to be 564.103 m/s. Thank you so much!
 
  • #10
aligass2004 said:
I finally figured it out. I used Yf = Yi + Vyi(t) + 1/2ay(t^2). Since the angle is zero because it's shot horizontally, the y component of velocity is zero, eliminating the middle term. So I just plugged in and got the time to be .078s. Then I used Xf = Xi + Vx(t). I found Vx to be 564.103 m/s. Thank you so much!

No prob. Good job!
 

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