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!

Another Projectile Motion

  1. Oct 15, 2005 #1
    Basketball player is 2m tall. He shoots at 40 degrees over a distance of 10m into a basketball net that is 3.05m. Whats the initial velocity.

    Theta=40 degrees

    Vxi = Vi cos(40) Ax=0 xi=0 xf=10
    Vyi= Vi sin(40) Ay=-9.80 yf=1.05 (difference between player and net)

    1. First I wanted to solve for time

    Xf = Xi + Vxi*t + (1/2)Ax*(t^2)
    10 = 0 + (Vi*cos(40))t + (1/2)(0) (t^2)
    10 = (Vi*cos(40))t

    t = (Vi*cos(40))/ 10

    2. Then, I'd use the Yf formula to plug my new time into to get Vi since Vyi= Vi sin(40)

    Yf = Yi + Vyi*t + (1/2)Ay*(t^2)
    1.05=0 + (Vi*sin(40))t - (1/2)(-9.80)(t^2)

    ---then substituting t into the 1.05=0 + (Vi*sin(40))t + (1/2)(-9.80)(t^2)
    and after all the algebraic dust settled I got ---

    Vi = 7.159.... the problem is the book says 10.7 m/s. Where did I go wrong??
    Last edited: Oct 15, 2005
  2. jcsd
  3. Oct 15, 2005 #2


    User Avatar
    Homework Helper
    Gold Member

    You have used too many "-"-s.
  4. Oct 15, 2005 #3


    User Avatar
    Homework Helper

    For the time, it should be,

    t = 10/(Vi*cos(40))
  5. Oct 15, 2005 #4
    that was a typo
  6. Oct 15, 2005 #5
    Holy crap... i'm staring at my page of work and you are sooooo right. Let me try that and see if it works now.:smile:
  7. Oct 15, 2005 #6
    It worked... It worked!!!

    That was the fix. I had the equation for t wrong. I got the 10.7 book answer now. Thank you sooooooooooo much!!!
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?