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Homework Help: Dynamics class w/o kinematics equations?

  1. Sep 9, 2014 #1
    1. The problem statement, all variables and given/known data
    My problem is I don't understand what my professor wants us to do instead. He says that we don't need to memorize any equations, namely the equations of motion, and that everything can be solved with basic principles and integration. The problem is, I have no idea how to solve even simple problems without the use of the equations of motion.

    Here's an example problem: Ball 1 is launched with an initial vertical velocity, V1=160 ft/sec. Three seconds later ball 2 is launched with an initial vertical velocity, V2. Determine V2 if the balls are to collide at an altitude of 300 ft.

    I know it's a simple question, and I know exactly how to do it using the equations of motion, but He says they are not necessary and that if we use the equations of motion we will get a zero on an exam for this question.

    2. Relevant equations

    He just says use v=ds/dt, and integrate each side and manipulate it and the answers will fall out. Can anyone enlighten me on how to solve this equation without using the equations of motion? Thanks.

    3. The attempt at a solution
  2. jcsd
  3. Sep 9, 2014 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper

    The equations of rectilinear motion weren't found under a bush by Newton. They can be derived in the special case for constant acceleration using simple integration, which you should be able to do if you have studied calculus.

    After all, if a = ds^2/dt^2 = dv/dt, how would you find v? If v = ds/dt, how would you find s?

    An added benefit to knowing how to derive the equations of motion for constant acceleration is also knowing what to do when the acceleration is not constant.

    One of the rules at PF about posting in the HW forums is that the poster should make an attempt at solution. Where is your attempt? If you want to just make complaints about your prof's teaching style, that is handled in another department.
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