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Homework Help: Displacement with and without friction

  1. Dec 5, 2011 #1
    1. When someone gets shot out of a human cannon with an initial velocity of 15 m/s and they have a mass of 60 kg. Final velocity is 0. Maximum constant force is 3000 N. This is free fall so acceleration is 10 m/s^2. There is no friction. So when you look at my attempt in solution I got the same answer as I did when I did this equation with friction because I did the same steps. So what is different about friction? How can I fix it?

    2. Relevant equations
    D=(Vi*T)=.5 (at^2)

    3. The attempt at a solution
    Well I did
    (15*1.5)+.5(10*1.5^2)= 22.5 +11.25=33.75.
  2. jcsd
  3. Dec 5, 2011 #2


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    Homework Helper

    Welcome to PF!
    I am bewildered by the question. What is actually going on? Are you shooting horizontally or vertically? When you say "Final velocity is 0." do you mean the person hits a brick wall or that the shot was a fizzle and he didn't make it out the end of the cannon? If he did get shot out and there is no friction, he would only have velocity zero when shot vertically and then only at the maximum height reached. Are we looking for the maximum height here? That is what your calculation applies to, except you have up and down both taken as positive directions in the second equation.

    It is so important to provide the exact wording of the question. Simplifications often make a problem impossible to solve.
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