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Homework Help: Grade 11 acceleration problem?

  1. Mar 3, 2010 #1
    1. The problem statement, all variables and given/known data
    Jack went up a hill to fetch water. Jack fell down and rolled down the hill accelerating at 0.65 m/s^2 down. If he rolled 11m down the hill in 3.7s, with what velocity was he moving when he fell?


    2. Relevant equations
    a = v2 - v1/t
    v2 = at + v1


    3. The attempt at a solution
    (0.65m/s^2)(3.7s) + 11
    = 13.5 m/s.

    I solved for v2, the velocity when he reached the bottom of the hill.
    However the answer says 1.8m/s.
    What am I doing wrong? Am I supposed to be looking for something else, not v2?
    Even if I solved for v1, I would get a negative answer.

    As usual, I am so confused. :yuck:
     
  2. jcsd
  3. Mar 3, 2010 #2
    try this
    [tex]R(t) = \frac{1}{2}at^2+v_it+R_i[/tex]
    [tex]v_i = \frac{R(t) - \frac{1}{2}at^2-R_i}{t}[/tex]
     
  4. Mar 4, 2010 #3
    That confuses me even more. What does R stand for?
     
  5. Mar 4, 2010 #4

    PhanthomJay

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    Science Advisor
    Homework Helper
    Gold Member

    what's that 11, that's a length unit, not a speed unit.
    you are supposed to be looking for the initial velocity when he fell.
    and what would the negative sign imply?
     
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