Physics Help Forum determine the force involving static coefficient

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 Oct 29th 2015, 07:21 PM #1 Senior Member   Join Date: Jun 2014 Posts: 306 determine the force involving static coefficient A force P acts as shown on a 200kg block placed on an inclined plane. The static coefficient of friction between the block and plane are Us= 0.5 . Determine the force of P to ensure he block is in the verge of moving down. The ans given is P = 560.4 N i have done in 2 ways , but my ans is incorrect .... why am i wrong ? 1. ) P cos 20 = Fs Pcos20 =0.5x9.81x200xcos10 P= 1028N 2. ) Wsin10 + P cos20 = 0.5x9.81x200xcos10 Pcos20 = 0.5x9.81x200xcos10 - Wsin10 Pcos20 = 0.5x9.81x200xcos10 – 200x9.81 sin10 P= 665.5N Attached Thumbnails
Oct 30th 2015, 01:01 AM   #2
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 Originally Posted by ling233 A force P acts as shown on a 200kg block placed on an inclined plane. The static coefficient of friction between the block and plane are Us= 0.5 . Determine the force of P to ensure he block is in the verge of moving down. The ans given is P = 560.4 N i have done in 2 ways , but my ans is incorrect .... why am i wrong ? 1. ) P cos 20 = Fs Pcos20 =0.5x9.81x200xcos10 P= 1028N 2. ) Wsin10 + P cos20 = 0.5x9.81x200xcos10 Pcos20 = 0.5x9.81x200xcos10 - Wsin10 Pcos20 = 0.5x9.81x200xcos10 – 200x9.81 sin10 P= 665.5N
i didnt mean to spam , anybody can help ?

 Oct 30th 2015, 07:11 AM #3 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,347 Your attempt #1 ignores the pull of gravity trying to pull the block down the incline, so is clearly incomplete. Your attempt #2 is correct, given the data provided. Are you sure you have correct value for the coefficient of static friction? Last edited by ChipB; Oct 30th 2015 at 07:16 AM.
Oct 30th 2015, 08:41 AM   #4
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Posts: 306
 Originally Posted by ChipB Your attempt #1 ignores the pull of gravity trying to pull the block down the incline, so is clearly incomplete. Your attempt #2 is correct, given the data provided. Are you sure you have correct value for the coefficient of static friction?
Yes, anything else wrong with my working?

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