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!

Freefall basketball problem

  1. Aug 14, 2015 #1
    Hello first time posting in the Physics forum!!

    1. The problem statement, all variables and given/known data

    A varsity player is attempting to make a shot. The ball leaves the hands of the player at an angle of 50 degrees to the horizontal at an elevation of 2 meters above the floor. The skillful player makes the shot with the ball travelling precisely through the center of the ring (8 meters from the player and 3 meters above the floor). To loud cheers, calculate the speed at which the ball left the hands of the player. Sketch the problem!

    2. Relevant equations
    Voy = Vosintheta
    Vox = Vocostheta

    3. The attempt at a solution
    Vox = Vocostheta -> 8=Vocos(50degrees) -> Vo=12.446m/s
    Then I plug it to X=Vot+1/2at^2 a is always 0 right? So it becomes X=Vot -> X=12.446(t) -> t=(0.643s)
    Then I plug the time to the y equation of free fall.. Delta Y is 1 right? Because 3-2=1
    Y=Vot-1/2gt -> 1=Vo(0.643)-1/2(9.8)(0.643)^2 Vo=4.7059m/s
    I'm not sure if my answer is right.. if not can someone guide me....
    If it is wrong sorry If I got a wrong answer.. This is why I post in this forums.
  2. jcsd
  3. Aug 14, 2015 #2


    User Avatar
    Science Advisor
    Homework Helper
    2017 Award

    Hello VZ, welcome to PF :smile: !

    Always a good idea to include dimensions in your calculations -- and to check them. In your case, you go off the rails in the very first line (sorry to say):

    ## 8 \;{\rm m} = V_{0,x} = V_0 \cos\theta \;{\rm m/s}## can never be right !

    Thing to do is write expressions for x(t) = 8 m and y(t) = 3 m, and eliminate t. Best to work with symbols until you have an expression for ##\theta##. Then check the dimensions and do the calculator work.

    Oh, and: strange you should ask if your answer is right: I see two answers for v0
  4. Aug 14, 2015 #3
    I don't know what you mean by dimension buuuuuuut..
    ΔX = Vo(t)
    ΔY = Vo(t)-1/2(g)(t)^2

    Do you mean that I should experiment with this two formulas? To get Vo? or to get t?
  5. Aug 14, 2015 #4
    First - you have equated horizontal velocity to horizontal displacement . This is wrong .
    So your second and third equations automatically become wrong .
  6. Aug 14, 2015 #5
    Yeap I realized that after sir BvU post. Sooooo if it is okay can you guide me in this question?
  7. Aug 14, 2015 #6
    Consider two unknowns v and t . Obviously v represents velocity of object , and t the time taken to reach the hoop .

    What you'll need to do is form two equations . Use the fact that horizontal velocity of object is v*cos(θ) and vertical v*sin(θ) .

    Can you manage the two equations ?
  8. Aug 14, 2015 #7
    Okay will do! I'll update you if I'm done. Thank you
  9. Aug 14, 2015 #8
    SIR I THINK I GOT IT. Okay here goes

    ΔX = Vox(t) right? bc a is always 0
    ΔX/Vox = t but we know that Vox=VoCos50 and ΔX = 8
    so 8/Vocos50 = t
    Voy=Vosin50 right?
  10. Aug 14, 2015 #9
    You need to substitute correctly for t .
  11. Aug 14, 2015 #10
    typo 8/Vocos50 but it is right the context is still there..
  12. Aug 14, 2015 #11
    Yes it is .
  13. Aug 14, 2015 #12


    User Avatar
    Science Advisor
    Homework Helper
    2017 Award

    No experimenting: you want to manipulate these two equations with two unknowns in such a way that you get one equation with one unknown, namely ##\theta##

    The way you write them is confusing -- one Vo with two different meanings, and Vo(t) makes it look as if Vo is a function of t --$$
    \Delta X = v_0 \cos\theta\; t \\ \Delta Y = v_0 \sin\theta\; t - {1\over 2} gt^2 $$ is a lot clearer. See also here

    [edit] oops, I'm lagging. This is in response to post #3 -- a bit late.
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: Freefall basketball problem
  1. Basketball problem (Replies: 7)

  2. Freefall Problems. (Replies: 5)