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!

A quarterback throws a football to a stationary receiver

  1. Apr 20, 2015 #1
    1. The problem statement, all variables and given/known data
    A quarterback throws a football to a stationary receiver 31.5m away from him. If the football is thrown at an initial angle of 40° to the ground, at what initial speed must the quarterback throw the ball for it to reach the receiver? What's the balls highest point during flight?

    2. Relevant equations
    ImageUploadedByPhysics Forums1429555553.253050.jpg

    3. The attempt at a solution
    ImageUploadedByPhysics Forums1429555747.953364.jpg

    I know this is only one small attempt at rearranging the formula, but trust me if you checked my trash you'd find crumpled up pieces of paper with many more attempts.

    I always go through the same procedure;
    1. I make my goal to find the initial velocity.
    2. To find initial velocity, I need time.
    3. To find time, I need /\y.
    4. To find /\y, I need the initial velocity.

    Please help.
     
  2. jcsd
  3. Apr 20, 2015 #2

    gneill

    User Avatar

    Staff: Mentor

    The motion has two dimensions: vertical and horizontal. Write the equations of motion w.r.t. time for both motions. The time that the football takes to reach its destination must be the same for both horizontal and vertical motions...
     
  4. Apr 20, 2015 #3
    I'm sorry, but could you please explain more in depth? I know there's two dimensions but set what two motions with which equations?
     
  5. Apr 20, 2015 #4

    gneill

    User Avatar

    Staff: Mentor

    The horizontal motion and the vertical motion. What are the equations for each?
     
  6. Apr 20, 2015 #5
    Oh, the /\y and /\x equations? I thought you referred to the x and y components of the velocity..

    Well, after trying to set them equal to eachother — it gets to a point where the /\t can't be really set equal to the rest of the /\y equation and you have a quadratic of a sort:
    ImageUploadedByPhysics Forums1429560546.830396.jpg
     
  7. Apr 20, 2015 #6

    gneill

    User Avatar

    Staff: Mentor

    The x and y components of the trajectory are independent equations in terms of time. Write them separately to begin with. (And it would be better if you would type them in rather than attaching image. Use icons in the editing window's top bar to make subscripts or superscripts: x2, x2. Other symbols and special characters can be found using the Sigma icon).

    You should then have a pair of equations that describe the motion with respect to time. The only unknowns will be the initial velocity and time. Two equations in two unknowns.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: A quarterback throws a football to a stationary receiver
  1. Football Throw (Replies: 11)

  2. Football Throw (Replies: 1)

Loading...