# Ballistics -- How deep does the bullet penetrate into the wood?

• duchuy
In summary, the problem is calculating the penetration distance of a firearm projectile in a tree using the equation d = mv^2 / 2C with given values of m = 20g, v = 300km/h, and C = 750 N. However, when entering the answer with two significant figures, it was incorrect. It turns out that the answer should be in cm instead of m.
duchuy
Homework Statement
How deep in a tree would a mass m firearm projectile penetrate at velocity v0 if the frictional force between the projectile and the wood is C ?
Relevant Equations
d = mv^2 / 2C
Hi, I was given this exercice where I have to calculate the penetration distance, knowing that m = 20g, v = 300km/h and C = 750 N and I have to give the results with two significant numbers. I really thought that all I had to do was replace the values so I did :
d = (20.10^-3) x (300/3,6)^2 / 2x750 and I ended up with d = 0,0925925925...
But when I entered the answer with two significant figures = 0,093, the answer was wrong.
Sorry if i have misused any term, I translated this from french.

duchuy said:
Homework Statement:: How deep in a tree would a mass m firearm projectile penetrate at velocity v0 if the frictional force between the projectile and the wood is C ?
Relevant Equations:: d = mv^2 / 2C

Hi, I was given this exercice where I have to calculate the penetration distance, knowing that m = 20g, v = 300km/h and C = 750 N and I have to give the results with two significant numbers. I really thought that all I had to do was replace the values so I did :
d = (20.10^-3) x (300/3,6)^2 / 2x750 and I ended up with d = 0,0925925925...
But when I entered the answer with two significant figures = 0,093, the answer was wrong.
Sorry if i have misused any term, I translated this from french.
It looks right. It might be two decimal places, rather than two significant figures. Or, the answer in cm?

duchuy
oh my god the answer is actually in cm, thank you so much! how'd you figure that out...?

berkeman
duchuy said:
oh my god the answer is actually in cm, thank you so much! how'd you figure that out...?
I'm clever with things like that!

berkeman, Steve4Physics and duchuy

## 1. How does the type of wood affect bullet penetration?

The type of wood can greatly affect bullet penetration. Softwoods, such as pine, are less dense and can be penetrated more easily than hardwoods, such as oak. The density and hardness of the wood can also impact the distance the bullet will travel within the wood.

## 2. Does the angle of entry affect the depth of bullet penetration?

Yes, the angle of entry can greatly impact the depth of bullet penetration. A bullet that enters the wood at a perpendicular angle will penetrate deeper than one that enters at an angle. This is because a perpendicular entry allows for more force to be concentrated on a smaller surface area, resulting in deeper penetration.

## 3. Can the velocity of the bullet affect its penetration into wood?

Yes, the velocity of the bullet can greatly impact its penetration into wood. A higher velocity bullet will have more kinetic energy, allowing it to penetrate deeper into the wood. However, if the bullet is traveling too fast, it may fragment or disintegrate upon impact, resulting in less penetration.

## 4. What other factors besides wood type and bullet velocity can affect penetration depth?

Other factors that can affect penetration depth include the shape and weight of the bullet, as well as the distance the bullet has traveled before hitting the wood. A heavier and more aerodynamic bullet will have greater penetration capabilities. Additionally, if the bullet has already traveled a significant distance, it may have lost some of its velocity and energy, resulting in shallower penetration.

## 5. Is there a way to accurately predict the depth of bullet penetration into wood?

While there are formulas and calculations that can estimate the depth of bullet penetration into wood, there are many variables that can affect the actual outcome. It is difficult to accurately predict penetration depth without conducting specific tests with the exact type of wood and bullet being used. Additionally, factors such as moisture content and density variations within the wood can also impact the results.

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