Physics Help Forum Trouble with exam prep question

 General Physics General Physics Help Forum

 Dec 17th 2017, 05:55 PM #1 Junior Member   Join Date: Dec 2017 Posts: 7 Trouble with exam prep question A stationary horizontal platform is free to rotate about its vertical axis. The radius of the platform is R=1.6m and its moment of inertia is 660 kgm^2. A 43kg boy jumps on the rim of the platform with the velocity of 2.2 m/s tangential to the rim. What will be the angular speed of the platform with the boy? I am helping my son prep for an exam. We have been given the answer of w=.197 rad/s, but we cannot figure out how that is correct. We have considered rotational kinetic energy of the platform and of the boy along with conservation of momentum, but no luck. Any assistance would be greatly appreciated. I am not a physics expert and can only help him so much.
 Dec 17th 2017, 09:45 PM #2 Senior Member   Join Date: Apr 2017 Posts: 153 The addition of the boy to the platform will change it's I to 660 + (43 x 1.6 x 1.6) The new I is 770 Initial energy in boy = 1/2 x 43 x2.2 x2.2 = 104 = 1/2 x 770 x (omega squared) Omega squared= 0.3106 Omega = 0.557 rad/sec
 Dec 18th 2017, 12:47 PM #3 Junior Member   Join Date: Dec 2017 Posts: 7 Thank you

 Tags exam, prep, question, trouble

 Thread Tools Display Modes Linear Mode

 Similar Physics Forum Discussions Thread Thread Starter Forum Replies Last Post HNCMATHS Advanced Mechanics 2 Apr 8th 2010 02:28 PM HNCMATHS Advanced Mechanics 1 Mar 9th 2010 03:08 PM C.E Advanced Thermodynamics 3 May 28th 2009 12:16 PM confused77 Special and General Relativity 0 Aug 23rd 2008 06:50 AM Heavyarms2050 Advanced Mechanics 5 May 3rd 2008 07:37 PM