Distance required

[Herjan]

Hi, Im new on this forum and I just want to ask a question that I asked in class and my teacher wants me to solve, and I guess this forum is full of clever people .

 

I was wondering how far up a bullet would have to be up in the air, for it to burn up before it reaches the ground.

 

In advance, thanks for the help.

[insane_alien]

do you know how fast it would have to be going to burn up? if you don't then we can't help you work it out.

[mr d]

a few items also to concider.

bullet type and size - caliber

bullet material - straight lead or full metal jacket .. etc

bullet shape - blut, rounded, pointed, hollow point

 

angle of bullet flight on reentry

 

mr d

[s pepperchin]

The escape velocity of the earth is the same for any mass so would the bullet be going faster than that escape velocity long enough to escape earth's gravity? Obviously thie answer to this is that the bullet doesn't maintatin the velocity long enough because if it was then there would no tbe stories about people who get hit in the head by stray bullets that have been fired into the air.

 

The easiest physics problem for path of the bullet would need just the mass and initial velocity of the bullet to solve, A more realistic problem would need the mass, initial velocity, coefficient of drag, cross sectional area of the bullet, position on the Earth from which the bullet was fired, etc....

[Klaynos]

Speculations (ignoring the fact the earth is spining and any tangential air resistance due to this):

 

surely the burnup is due to friction

=>friction is preportional to velocity

=>the greatest friction is at the greatest speed

=>the greatest velocity of a bullet going *streight* up is immidiately after launch

...

[swansont]

Speculations (ignoring the fact the earth is spining and any tangential air resistance due to this):

 

surely the burnup is due to friction

=>friction is preportional to velocity

=>the greatest friction is at the greatest speed

=>the greatest velocity of a bullet going *streight* up is immidiately after launch

...

 

 

Burnup of objects falling to the earth is largely from ram pressure — the atmosphere can't get out of the way and compresses, and as it does so it heats up.

[[Tycho?]]

As the topic starter is probably starting to realize, there is no quick or easy answer to this question. It depends on a wide variety of variables and other bits of information not easily attained. I dont see how your teacher expected you to solve this without much more information.