Question 1

Author Message   Lau Kai Kwong Username: lkk Registered: 04-2003 Posted on Sunday, April 13, 2003 - 12:27 am:    A rod of mass m rests in the angle between a smooth vertical wall and a smooth plane inclined at 30° to the wall. Find the thrusts of the rod on the wall and the plane. Please post your solution.   971041 Username: 971041 Registered: 04-2003 Posted on Tuesday, April 15, 2003 - 03:25 pm:    force along the plane: R sin 30° = mg sin 60° R 1/2 = mg √3/2 R = √3 mg R = r sin 60° √3mg = r √3/2 2mg = r   971041 Username: 971041 Registered: 04-2003 Posted on Tuesday, April 15, 2003 - 03:45 pm:    都係咁好d mg/ r = cos 60° mg = r (1/2) r = 2 mg R = r sin 60° = 2 mg (√3/2) = √3 mg   971041 Username: 971041 Registered: 04-2003 Posted on Tuesday, April 15, 2003 - 03:46 pm:    ai........ fig. 點 post的????   Lau Kai Kwong Username: lkk Registered: 04-2003 Posted on Tuesday, April 15, 2003 - 06:44 pm:    Type \image{description}, you will be asked to upload the figure then. See Formatting for further information.   Lau Kai Kwong Username: lkk Registered: 04-2003 Posted on Tuesday, April 15, 2003 - 06:47 pm:    Please post the force diagram, as I cannot determine whether you are correct without the diagram. Thanks.   971041 Username: 971041 Registered: 04-2003 Posted on Tuesday, April 15, 2003 - 06:58 pm:    description---->咩意思????   971041 Username: 971041 Registered: 04-2003 Posted on Tuesday, April 15, 2003 - 07:48 pm:      Lau Kai Kwong Username: lkk Registered: 04-2003 Posted on Tuesday, April 15, 2003 - 09:02 pm:    Quite good. But... 1. your figure is too inaccurate... 2. you would better state something like "By resolving forces horizontally" or "By resolving forces vertically". 3. you would better use capital letters for forces, and small letters for distances. 4. you should write R = 2mg instead of 2mg = R. Anyway, the first 3 lines of your solution (R' is used instead of r) would better written as: By resolving the forces vertically, R' cos60° = mg R' = 2mg