1. Not finding help here? Sign up for a free 30min 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!

Maximum range of a projectile when launched at 45°(Physics by example, Rees, pr. 14)

  1. Jan 31, 2012 #1
    [​IMG]

    In this solution the t in the y-coordinate equation is substituted using the x-coordinate equation and ultimately leads to the answer.

    My questions:
    1. Why don't I get the same answer when I substitute the v or v and t instead?
    2. How am I supposed to know to substitute t in this example and not v?
     

    Attached Files:

  2. jcsd
  3. Jan 31, 2012 #2

    Delphi51

    User Avatar
    Homework Helper

    Re: Maximum range of a projectile when launched at 45°(Physics by example, Rees, pr.

    I don't see how you can get it by keeping the t. You don't know t, so how can you tell the maximum value of x that way? I get
    x = gt²/(2*tanΘ)
    and can't tell what combination of t and Θ provide the maximum x.
    It would be good to see your calc.

    There is no need to eliminate the v; it is a constant. But you must eliminate the variable t.
     
  4. Jan 31, 2012 #3
    Re: Maximum range of a projectile when launched at 45°(Physics by example, Rees, pr.

    Well, the problem is quite easy to approach.
    Range is given by u^2 sin(2a) / g, where a is the projection angle.
    Since -1<sin a<1, the max. value for a sine function = 1. This occurs when the angle is 90 degrees or .5pi radians.
    So, for a fixed u:
    2a = 90
    a = 45 degrees.
     
  5. Jan 31, 2012 #4
    Re: Maximum range of a projectile when launched at 45°(Physics by example, Rees, pr.

    Ok, now I understand. Thnx!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Similar Discussions: Maximum range of a projectile when launched at 45°(Physics by example, Rees, pr. 14)
Loading...