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Homework Help: Dynamics problem

  1. Oct 7, 2014 #1
    • Warning! Posting template must be used for homework questions.
    this is a part of a much bigger problem, I have a 600lb motorcycle going from point A to point B, which are 500 ft apart, i know the force exerted by the road on the motorcycle when the throttle is pressed is F(t)=300(1-.1t).
    I need time in order velocity at B ,
    I'm really lost on where to start on this, i was thinking f=ma could give me acceleration, but then i dont know what to do with that.
  2. jcsd
  3. Oct 7, 2014 #2
    Are you trying to determine the velocity at point B?

    If you know the acceleration then by definition you should be able to get the velocity.
  4. Oct 7, 2014 #3
    so f=ma will give me a acceleration as a function of t, and yes i need velocity at B, but then won't i only have velocity as a function of t if by definition?.
  5. Oct 7, 2014 #4


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    Right, but if you have velocity, you can find position. Find how long it takes to get to point B, then use that t for your velocity.
  6. Oct 7, 2014 #5


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    Gee, if only there were a way that acceleration could be used to get velocity, and that velocity could then be used to find distance. It would seem to be a good reason to study rectilinear motion in physics, or something. Maybe somebody wrote a textbook on how to do this stuff. IDK, that would probably take a lot of work to figure out.
  7. Oct 7, 2014 #6
    so would i use Vi^2=Vf^2+2A(500) and substitute in V and A as their function of t equations? because then i get t= 10.05 does that seem right?
  8. Oct 7, 2014 #7


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    What units are you using for m, F, and distance? I hope F is in ft/lbs.
  9. Oct 7, 2014 #8
    m = slugs, F lbs, distance = ft
  10. Oct 7, 2014 #9


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    No, that formula only works for constant acceleration. You need to use the general relationships between acceleration, velocity, and distance - namely, integral formulas.
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