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: What is the impulse on the ball from the wall?

  1. Mar 19, 2008 #1
    1. The problem statement, all variables and given/known data

    a 250 g ball with a speed v of 6.6 m/s strikes a wall at an angle θ (the angle between the wall and the path of motion) of 30° and then rebounds with the same speed and angle. It is in contact with the wall for 6 ms. What is the impulse on the ball from the wall?


    2. Relevant equations

    J is the impulse
    J = mvfinal - mvinitial
    the change in momentum (P) = Jnet
    P = mv


    3. The attempt at a solution

    First I broke the velocity vectors into components:

    6.6m/s * cos(30) = 5.716m/s
    6.6m/s * sin(30) = 3.3 m/s, so

    Vo = 3.3i + 5.716j (m/s)
    and
    Vfinal = 3.3i - 5.716j (m/s)

    and the momentum of each is the mass of the object * the velocity:

    (.25kg)Vo = Po = .825i + 1.428j
    (.25kg)vfinal = Pfinal = .825i - 1.428j

    so Jnet = Pfinal - Pinitial = (.825-.825) i + (-1.428 -1.428)j
    so Jnet = -2.856 in the j direction
    so the answer should be -2.856, but it is not (and it is not 2.856 either)...

    any help is appreciated.
    Thanks!
     
  2. jcsd
  3. Mar 20, 2008 #2
    Have a re-look at your v(initial).
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook