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Homework in physics (average force and momentum)

  1. Aug 25, 2010 #1
    The problem statement, all variables and given/known data

    A 1000 kg car strikes a tree at 30 km/hr & comes to a stop in 0.15s. Find its initial momentum and the average force on the car while it is being stopped.

    Attempt at a solution

    For velocity,

    I tried converting 30 km/hr to m/s

    30 km/hr * 1hr/3600s*1000m/1km

    =30000 m/ 3600 s = 8.33 m/s

    For the momentum...

    p = mv

    p = 1000 kg (8.33 m/s)

    p = 8330 kg * m/s

    Is this correct? How do I find the average force? Please help me. My teacher says I'm wrong at some equation.
  2. jcsd
  3. Aug 25, 2010 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Everything you've done so far is correct. To find the average force, consider the impulse delivered by the tree.
  4. Aug 25, 2010 #3
    how do I solve for that? We are only given the mass, velocity and the time.
  5. Aug 25, 2010 #4

    Doc Al

    User Avatar

    Staff: Mentor

    You have all you need. What's the definition of impulse? Look up the impulse-momentum theorem. You'll set up an equation and solve for the force.
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