Calculating Frictional Force on a Bullet Using the Momentum Formula

[nrc_8706]

a rifle fires a(n) 6g bullet with a muzzle velocity of 390m/s into a block of wood. the bullet comes to rest after it has made a(n) 18cm deep hole in the wood. what is the magnitude of the average frictional force slowed the bullet?

can i use this formula?
J=FT=pf-pi=mv

 

[Doc Al]

You could, but you'd first have to figure out the time. Instead, consider the work done by the frictional force on the bullet.

 

[Tide]

What would you use for the time?

I suggest asking yourself how much work the frictional force does.

 

[nrc_8706]

is it W=Kf-Ko ?

 

[andrewchang]

yes, but make sure not to forget that the work done by friction will be negative.

 

[nrc_8706]

so...W=1/2mVf^2-1/2mVo^2 does Vf cancel since it comes to rest?

 

[andrewchang]

yes, it does

 

[nrc_8706]

the answer is W=456.3 is that all?

 

[andrewchang]

you've found the work, but the question wants to know the force. so what is the equation for work?

 

[nrc_8706]

is it W=Fd

 

[andrewchang]

yes, that's right

 

[nrc_8706]

Thank You So Much!