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Homework Help: Vectors, Forces Accelerating a Train

  1. Oct 22, 2009 #1
    If anyone could help me with these two questions that would be great.

    1.A freight train has a mass of 1.20E+7 kg. If the locomotive can exert a constant pull of 8.03E+5 N, how long does it take to increase the speed of the train from rest to 70.6 km/hr?

    2.A football punter kicks a football from rest so that it attains a speed of 14.0 m/s during the time in which his toe is in contact with the ball (about 0.29 s). If the football has a mass of 0.520 kg, what average force (in N) does the punter exert on the ball?
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Oct 22, 2009 #2
    It still disgusts me how a lot of physics textbooks make students do numerical calculations instead of general solutions. That aside...

    Both questions are talking about a CHANGE IN VELOCITY. What is the change in velocity called? Hint: It's called acceleration, shhhh don't tell.

    For question 1:
    If you accelerate at a constant rate for some time, what is your velocity (that is, how does velocity depend of time, given that acceleration is constant? Your textbook most likely answers this, look up "kinematic equations" if you can't find it.) After figuring this out, ask yourself how force, mass, and acceleration are related, Mr. Newton.

    For question 2:
    The basic idea of the question is the same as question one, except now you know the time, velocity, and force, instead of the force, mass, and velocity. Just think of how the four variables (F, m, a, v) are related.

    I hope this helps you. If you have any further questions with this or other problems, feel free to post or PM them.
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