Finding force(N) wood has against the bullet

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Homework Help Overview

The discussion revolves around a physics problem involving a 22.0-caliber rifle bullet penetrating a block of soft wood. The bullet's mass is given as 1.80 g, and it travels at a speed of 320 m/s before striking the wood, which is fixed in place. The problem asks for the force exerted by the wood on the bullet, assuming a constant retarding force during penetration to a depth of 0.140 m.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss calculating the acceleration of the bullet and the resulting force using Newton's second law. There is uncertainty about the sign of the force and whether it should be reported as negative or positive. Some participants suggest using energy considerations, specifically the relationship between work done and kinetic energy loss, as an alternative approach.

Discussion Status

The discussion includes various attempts to clarify the calculations and the implications of the retarding force. Some participants express confidence in their calculations while others question the assumptions made regarding the force's direction and the significance of significant figures. There is no explicit consensus on the final answer, but multiple lines of reasoning are being explored.

Contextual Notes

Participants note the importance of significant figures in their calculations and the need to ensure that assumptions about the retarding force are clearly understood. There is also a mention of the energy approach as a potentially simpler method for solving the problem.

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Homework Statement



22.0-caliber rifle bullet of mass 1.80 g, traveling at 320 m/s strikes a block of soft wood, which it penetrates to a depth of 0.140 m. The block of wood is clamped in place and doesn't move. Assume a constant retarding force.

What force, in Newtons, does the wood exert on the bullet?

Homework Equations


The Attempt at a Solution

Long story short, acceleration is -365714.29 m/s^2

Is it really as simple as .0018*-365714.29 = -658.29 N ? Or maybe 658.29 N since the force of the wood on the bullet is opposite of the bullet on the wood?

Since Fnet = ma
 
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Crusaderking1 said:

Homework Statement



22.0-caliber rifle bullet of mass 1.80 g, traveling at 320 m/s strikes a block of soft wood, which it penetrates to a depth of 0.140 m. The block of wood is clamped in place and doesn't move. Assume a constant retarding force.

What force, in Newtons, does the wood exert on the bullet?


Homework Equations





The Attempt at a Solution




Long story short, acceleration is -365714.29 m/s^2

Is it really as simple as .0018*-365714.29 = -658.29 N ? Or maybe 658.29 N since the force of the wood on the bullet is opposite of the bullet on the wood?

Since Fnet = ma

It is that simple [I hope you a value is correct; I haven't checked]

The question referred to a retarding force, so easiest just to answer "The retarding force is 658N" watch the significant figures in your final answer - you use all the figures i your calculations]
 
Crusaderking1 said:
Long story short, acceleration is -365714.29 m/s^2

Is it really as simple as .0018*-365714.29 = -658.29 N ? Or maybe 658.29 N since the force of the wood on the bullet is opposite of the bullet on the wood?

Since Fnet = ma
You might find it easier to use energy: the work done by the wood on the bullet is equal to the loss of kinetic energy. So:

F = KE/d

AM
 
PeterO said:
It is that simple [I hope you a value is correct; I haven't checked]

The question referred to a retarding force, so easiest just to answer "The retarding force is 658N" watch the significant figures in your final answer - you use all the figures i your calculations]

Thanks.
 
Andrew Mason said:
You might find it easier to use energy: the work done by the wood on the bullet is equal to the loss of kinetic energy. So:

F = KE/d

AM

Never thought about that! thanks, that would make it easier.
 

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