Physics Help Forum Sledgehammer falling on pivot. physics question. Where are my workings wrong?

 Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum

 Nov 29th 2010, 06:00 PM #1 Junior Member   Join Date: Nov 2010 Posts: 3 Sledgehammer falling on pivot. physics question. Where are my workings wrong? A sledgehammer with a mass of 2.80 kg is connected to a frictionless pivot at the tip of its handle. The distance from the pivot to the center of mass is r_cm=0.560 m, and the moment of inertia about the center of mass is I_cm = 0.0410 kgm2. If the hammer is released from rest at an angle of theta=45.0 degrees such that H=0.396 m, what is the speed of the center of mass when it passes through horizontal? OK, so using parallel axis theorem: I = Icm + Md^2 = 0.91908 gives me moment of inertia at the pivot plug that into the energy equations gravitational potential energy (initial) = Kinetic energy (final) mgH = (1.2)(I)(w^2 ) finding for w = 23.67 So now that I have omega I can find linear speed by using v=rw where r is the distance to the CM/ v = 13.3 m/s When I enter this answer in the assignment however it's wrong. Can anyone tell me where I messed up? Thanks!
 Nov 29th 2010, 10:22 PM #2 Member   Join Date: Oct 2010 Location: Sri Lanka Posts: 63 I think what you have taken as w is really the w^2
 Nov 30th 2010, 01:00 PM #3 Junior Member   Join Date: Nov 2010 Posts: 3 Actually looks like I just did the calculation for w wrong. Should of got 9.86 as w^2.

 Tags falling, physics, pivot, question, sledgehammer, workings, wrong

 Thread Tools Display Modes Linear Mode

 Similar Physics Forum Discussions Thread Thread Starter Forum Replies Last Post FistLength Thermodynamics and Fluid Mechanics 1 Jan 22nd 2014 05:33 AM tmac20 Kinematics and Dynamics 1 Sep 30th 2013 11:59 AM kinhew93 Kinematics and Dynamics 2 Jan 20th 2013 02:38 AM whmische Light and Optics 3 Dec 21st 2011 02:05 AM kingman Kinematics and Dynamics 3 Jun 28th 2010 11:33 AM