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Homework Help: Work/ kinetic energy theory

  1. Oct 27, 2011 #1
    1. The problem statement, all variables and given/known data

    A 5.75 kg object passes through the origin at time t = 0 such that the x component of velocity is 5.00 m/s and its y component of velocity is -3.00m/s.

    a) what is the kinetic energy of the object at this time?

    b) at t = 2.00s, the particle is located at x = 8.50m and y = 5.00m. What constant force acted on the object during this time interval?

    2. Relevant equations

    Change in K = Kfinal - Kinitial
    where K = 1/2 * m * v^2

    W= force * displacement

    3. The attempt at a solution

    I got part a by finding the magnitude of the object's velocity then plugging my known values into the K = 0.5mv^2 equation. I got my answer to be K = 97.8J at t=0.

    I'm a bit lost on what to do for part b though...
  2. jcsd
  3. Oct 28, 2011 #2
    You can compute how far the object traveled in 2 seconds. You know its speed at time = 0. Does this information suggest any other equation you might use to compute the average acceleration?

    Knowing the average acceleration, you can compute the constant force.
  4. Oct 28, 2011 #3


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    Homework Helper

    If the velocity had been unchanged for the 2 seconds, the object will have moved 10.0 in the x direction, and -6 in the y direction.

    Instead it ended up where they said.

    Treat each dirction separately to find the acceleration in the x-direction and y-direction. COmbine them to find the overall acceleration.

    F = ma should give the required force.
  5. Oct 30, 2011 #4
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