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Homework Help: Change in Linear Momentum with mass and velocity

  1. Oct 17, 2008 #1
    1. The problem statement, all variables and given/known data

    A 2700 kg truck traveling north at 37 km/h turns east and accelerates to 47 km/h.

    (a) What is the change in the truck's kinetic energy?

    (b) What is the magnitude of the change in the linear momentum of the truck?

    (c) What is the direction of the change in the linear momentum of the truck?
    __° (measured clockwise from east)

    2. Relevant equations

    p = m * v

    3. The attempt at a solution
    Part A is easy enough, i found it to be around 88450 J.

    Part B, finding the change in momentum, I tried (m * v) - (M * V), with the latter part being the final speed (after converting to m/s), and got an answer of 7400 kg*m/s, which was wrong. I don't see why this doesn't work, so any explination would be much appreciated.

    Part C, I have no clue.. I don't remember seeing any formulas with angles in them.. after searching google i found some confusing looking formulas that have to do with angular momentum, but the problem specifically says linear.. so any insights on that would be appreciated as well, thanks.
  2. jcsd
  3. Oct 17, 2008 #2
    You're messing this up because momentum is a vector! Find the magnitudes of the initial and final momentum -- but then don't just subtract! Make a diagram and do the vector math (it will involve trig functions).
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