Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    User Avatar
    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?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook