1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Random projectile motion problems.

  1. Sep 8, 2009 #1
    1. Trajectory of a projectile is modeled by
    [tex]r(t) = x(t)i+y(t)j[/tex]
    [tex]x(t) =at^2+bt[/tex]
    [tex]x(t) =ct+d[/tex]
    It asks for the displacement between t = 1 and t=3 s.
    And I got
    If it is asking for the displacement would the answer be[tex] x+y [/tex] or [tex]\sqrt{x^2+y^2}[/tex]?

    2. The ball falls down from height h (above incline) on incline with angle 45. Calculate how far from striking point, ball will hit incline again if collision is perfectly elastic.

    So the velocity it gains from falling would be [tex]\sqrt{2gh}[/tex]. That would be the initial velocity of when it reflects at 0 degrees. Then you could create the projectile motion equations for it.
    It will land when the x and y distances are equal. So after replacing the y with x, solving for t in terms of x, and substituting I got x=4h=y. So then the displacement would be [tex]\sqrt{8}h[/tex]. That right?
    Now I originally did this as the ball reflecting at 45(><) and i got [tex]x=hcos^2\theta (tan^2\theta - 1)[/tex] That gives you zero but you know that it would eventually hit the ground, why is that?
    Last edited: Sep 8, 2009
  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted