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The force of friction moving up a slope

  1. Oct 19, 2008 #1
    A grocery cart is being pushed with a force of 450 N at an angle of 30.0 degrees to the horizontal. If the mass of the groceries is 42 Kg,
    (a) Calaculate the force of friction if the coefficient is 0.60.

    Alright guys I have been doing this problem for around two hours. My physics teacher isn't a good teacher and I have no idea how to get the right answer(located in the back of book).

    Ive tried all I can think of,
    Ff= (0.60)(450n)
    = 270n

    450 COS 30
    = 389.7 N
    and a bunch of othe stuff I erased off my paper

    The answer in the back is 3.8 x 102 or around 380 n
  2. jcsd
  3. Oct 19, 2008 #2


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    What is the mass of the cart and groceries?
  4. Oct 19, 2008 #3
    it doesn't say just assume 42kg I geuss
  5. Oct 20, 2008 #4


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    The 450 N force has 2 components. There is the Cos30 component forward, but there is also the Sin30 component down. Sin30*450 N + 42*(9.8) N = 225 + 411.6 N = 636.6 N in the downward direction.

    Then you use your coefficient of friction based on the total downward force.
  6. Oct 20, 2008 #5
    yah, thanks. I figured it out last night. I drew a diagram
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