 Nov 17th 2012, 12:04 PM #1 Junior Member   Join Date: Nov 2012 Posts: 1 angular momentum I am in college taking a physics class and for some reason i am having a problem with these equations so any help would be appreciated. here is the question and where i am with the solutions. a .005 kg bullet traveling horizontally at 1 X 10^3 m/s strikes an 18 kg door imbedding itself 10cm from the side opposite the hinge of this 1 meter door.the hinge is frictionless. (a) before the bullet hits does it have angular momentum--- this answer i got it does with reference to the hinge point. (b) evaluate the angular momentum--- so i started out with momentum equation mv(bullet) + mv(door) = ((m(bullet) + m(door) v(final) the mvdoor is 0 so i solved for initial momentum of bullet and got 5kgm/s according to our physics book we now multiply both sides by r to get angular momentum (r x P) where r is the perpendicular r. so r is .9 meters so i multiply that by 5kg(m)/s and get 4.5kg(m)/s and this is the correct answer. (c) is the mechanical energy of the bullet door system constant during collision ? answer no it loses some do to internal energy. (d) This question is where i got lost so i dont know if i am over thinking it or not. At what angular speed does the door swing open immediately after the collision. angular speed(w) = velocity(v)/radius(r) so my problem is angular momentum is Iw and in the previous momentum equation by me multiplying both sides by r the book says that makes it angular momentum so i have 4.5 kg(m)/s = Iw divide both sides by I(moment of inertia). So do i have to solve for moment of inertia? do I use the parallel axis theorem on the door and treat it like a bar? this is where i get confused? any help is extremely appreciated?  Tags angular, momentum Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Similar Physics Forum Discussions Thread Thread Starter Forum Replies Last Post roshanhero Advanced Mechanics 0 Sep 8th 2013 11:26 PM anMoons Advanced Mechanics 0 Jan 19th 2009 07:22 AM anMoons Advanced Mechanics 0 Jan 19th 2009 07:19 AM anMoons Advanced Mechanics 0 Jan 19th 2009 07:11 AM devanlevin Advanced Mechanics 0 Jan 3rd 2009 01:29 PM