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Homework Help: Speed before impact of an object falling down a slope.

  1. Nov 23, 2009 #1
    1. The problem statement, all variables and given/known data
    A 4.7 kg block is placed on an incline with a 14° angle.
    Ignoring friction, what is the acceleration of the block?
    If the coefficient of kinetic friction is 0.25 (and has overcome static friction) what is the acceleration of the block?
    If the incline is 4.6m long, what is the velocity of the block at the bottom (considering friction)?

    2. Relevant equations
    Force on block due to gravity = 11.15N
    3. The attempt at a solution
    To find the first part, I used Fnet=ma, rearranged to find a and found the acceleration without friction to be:
    FgSinθ/m = 46sin14°N/4.7kg = 2.36m/s^2

    Then I calculated Ff to be 11.18N, which means there is no movement, and that is where I'm stumped because the last question would lead one to think that it moved somewhat.
  2. jcsd
  3. Nov 24, 2009 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper

    If the net force is zero, that means the acceleration is zero. It can still be moving (has velocity not zero).
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