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Homework Help: Calculating Distance and Time given mass,velocity,and Force.

  1. Jan 27, 2010 #1
    1. The problem statement, all variables and given/known data
    A power boat of mass 475 kg is cruising at a constant speed of 8.9 m/s. The propeller provides a drive force of 765 N. The driver of the boat shuts off the engine, and the boat coasts to a halt. Assume-contrary to fact-that the resistive force due to the water is constant, independent of the boat's speed.

    2. Relevant equations
    F=ma
    a=velocity/time
    v=d/t

    3. The attempt at a solution
    I divided Force by mass to get acceleration since F=ma.
    Then using the acceleration formula a=d/t i calculated time.
    Using that time i calculated distance useing the velocity formula v=d/t.
    I got 49.183 meters and 5.526 seconds.
    I got this answer wrong.
     
  2. jcsd
  3. Jan 27, 2010 #2
    Your formula for acceleration is not correct. Look up the "kinematics equations" to get the time and the distance. You'll need to think about the boat's final velocity to use one of the kinematics equations.
     
  4. Jan 27, 2010 #3
    but i can't figure out how to calculate acceleration because i need distance and time.
     
  5. Jan 27, 2010 #4
    you already said how to find acceleration! F = ma!
     
  6. Jan 27, 2010 #5
    thank you very much!
     
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