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Homework Help: Net force and acceleration

  1. Nov 26, 2003 #1


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    I'm doing some problems I found here:


    A car is moving at a constant velocity of 20 km/h (5.56 m/s). How much net force is required to raise its velocity to 50 km/h (13.89 m/s) in 30 seconds? Suppose the car has a mass of 150 kg.

    I used F= (150kg)([13.89m/s-5.56m/s]/30s)
    and got 41.65 N but apparently that's wrong. What am I doing wrong?
    Last edited by a moderator: Apr 20, 2017
  2. jcsd
  3. Nov 27, 2003 #2

    Doc Al

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    Staff: Mentor

    The only thing you're doing wrong is writing your answer with too many significant digits. :smile: Round off to two digits.
  4. Nov 27, 2003 #3


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    Ha! My phsycis teacher doesn't make us use significant figures (chem teacher did last year) so I completely forgot to do that :P
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