Calculating Acceleration in a Rifle-Bullet System

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Homework Help Overview

The discussion revolves around calculating the acceleration of a rifle when a bullet is fired. The rifle has a mass of 5.0 kg, and the bullet, initially stated as 2.0 g, has an acceleration of 2900 m/s². Participants are exploring the relationship between the forces acting on both the rifle and the bullet.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants are attempting to apply Newton's second law (F=ma) to relate the forces and accelerations of the rifle and bullet. Questions arise regarding unit consistency, particularly the conversion of the bullet's mass from grams to kilograms. Some participants express confusion about the relationship between force and acceleration.

Discussion Status

The discussion is ongoing, with participants questioning assumptions about mass and units. Some guidance has been offered regarding the need to convert units for proper calculations, and there is a recognition of the need to equate the forces acting on the rifle and bullet. Multiple interpretations of the problem are being explored.

Contextual Notes

There is a noted confusion regarding the mass of the bullet, which is initially given in grams, and the requirement to use consistent SI units throughout the calculations. Participants are also grappling with the implications of firing dynamics and the forces involved.

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Homework Statement



A rifle with a mass of 5.0kg fires a bullet with the mass of 2.0g.The bullet has an acceleration of 2900m/s^2. What is the acceleration of the rifle?

Homework Equations



I am pretty sure I have honed in on the formula to use, I am not sure how to use it though.

Also, is acceleration force?

The Attempt at a Solution



M=5.0kg
M=2.0g
A or F=2900

a=f/m or f/m=a

fyi: /sign is over.

Thank you
 
Last edited:
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Justhelp said:

Homework Statement



A rifle with a mass of 5.0kg fires a bullet with the mass of 2.0kg.The bullet has an acceleration of 2900m/s^2. What is the acceleration of the rifle?

Homework Equations



I am pretty sure I have honed in on the formula to use, I am not sure how to use it though.

Also, is acceleration force?

The Attempt at a Solution



M=5.0kg
M=2.0KG
A or F=2900

a=f/m or f/m=a

fyi: /sign is over.

Thank you

Force is not acceleration. They are related by the equation F=ma.

And I'm pretty sure that you have a typo for the mass of the bullet. Morel likely it is 2g = 0.002kg, right? Otherwise, that is one honkin' big bullet for that gun!
 
F=MA if that is it and seems more like it then it would work out to
F= 5.0kg(2900m/s^2)

=14500...but it's not asking for the force but the acceleration of the rifle... so the formula is switched around a bit. hm...
 
Is it bullet mass x bullet acceleration? That would be 5800 the force of the bullet right?
Then the formula moves around to become a=f(m), a=5800(5.0) a=29000 now.
 
And.. the mass of the bullet is 2.0g. Whoops.
 
Justhelp said:
F=MA if that is it and seems more like it then it would work out to
F= 5.0kg(2900m/s^2)

=14500...but it's not asking for the force but the acceleration of the rifle... so the formula is switched around a bit. hm...

You are close. They are assuming that the rifle is not supported by a shooter or anything as the bullet is fired. They want you to equate the forces of the rifle on the bullet and the bullet on the rifle. So you are given the mass and acceleration of the bullet -- what does that give you for the force of the rifle on the bullet?

Then use that force as the force of the bullet on the rifle -- you know the mass of the rifle, so what does that give for its acceleration?

They are trying to illustrate how given the same force, the acceleration depends on the mass...
 
"Then the formula moves around to become a=f(m), a=5800(5.0) a=29000 now."

29000m/s^2 right?
 
Justhelp said:
"Then the formula moves around to become a=f(m), a=5800(5.0) a=29000 now."

29000m/s^2 right?

I don't understand what you posted. What is the force that you get from the bullet's acceleration and mass?
 
f=(2g)(2900m/s^2) = 5800 the force of the bullet, then I did this accel= fm

a=5800(5.0)
 
  • #10
Justhelp said:
f=(2g)(2900m/s^2) = 5800 the force of the bullet, then I did this accel= fm

Check your units. You cannot multiply grams and m/s^2 -- you need to keep the masses in kg...

(and label the answer with the units of Newtons 1N = 1kgm/s^2)

When you get the force answer, calculate the acceleration of the rifle...
 
  • #11
the mass is grams... I'm confused. If I can't multiply m/s^2 with gram then what can I do? Do I use the 5.0kg instead?
 
  • #12
Justhelp said:
the mass is grams... I'm confused. If I can't multiply m/s^2 with gram then what can I do? Do I use the 5.0kg instead?

You need to work in a consistent set of units. The SI units that you will typically use for intro physics problems is meters, kilograms, seconds (mks). You need to keep all of your masses in kilograms, in order to be able to get the right answers.

So if the bullet's mass is 2g, what is that mass in kg? And proceed...
 
  • #13
F=MA
F= 5.0kg(2900m/s^2)

=14500 is the force of the rifle? I have to still use that number? Earlier I had assumed you meant that that was wrong.
 
  • #14
Does this mean the 2.0g has to be translated into Kg?
 
  • #15
and what I had had was correct? heh... but just not the unit.
 
  • #16
Justhelp said:
F=MA
F= 5.0kg(2900m/s^2)

=14500 is the force of the rifle? I have to still use that number? Earlier I had assumed you meant that that was wrong.
That is not correct or logical. You are mixing the mass of the rifle and the acceleration of the bullet. They have nothing to do with each other...

Justhelp said:
Does this mean the 2.0g has to be translated into Kg?
Yes.

Justhelp said:
and what I had had was correct? heh... but just not the unit.

What you had (see below) was correct for the force of the rifle on the bullet, if you convert the 2g mass into its equivalent mass in kg...

Justhelp said:
f=(2g)(2900m/s^2) = 5800 the force of the bullet,
 
  • #17
AH! ok, I didn't know that m/s^2 could not be multiplied by g, only kg mass. Sorry for any frustration.
 

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