-- The numbers for the speeds of the bullet going in and coming out
mysteriously disappeared, leaving the question looking quite absurd.
-- I might have been able to write an equation for the force you're
looking for, in terms of the unknown speeds, but I think we still need
to know either the thickness of the bag or else the length of time the
bullet stayed in it. I can't swear to it, but I'm pretty sure that even if
we knew the two speeds, we still couldn't find the friction force with
the information that's given.
When you look at it closely, the ONLY given information is the mass
of the bullet. You're pretty stingy with your info there, Alfie.
