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!

Homework Help: Momentum and impulse of a volleyball

  1. Nov 9, 2008 #1
    OK I have 1 more question for today...

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

    A 0.45kg volleyball travels witha horizontal velocity of 3.2m/s over the net. You jump up an hit the ball back witha horizontal velocity 7 m/s. If the contact time is 0.047s, what is the average force on the ball?

    2. Relevant equations


    Here are all the equations that were in our notes for this section.
    p (momentum) There was triangle P and triange t in my notes, so I wrote "change in"

    p=mv
    f=ma
    f*"change in"t="change in"p
    f*"change in"t=mvf-mvi
    "change in" P=mvf-mvi

    3. The attempt at a solution
    Again, I wasnt really sure what equation to use...

    [(.45kg)(-3.8m/s)-(.45kg)(3.2m/s)]/(.047s)

    I got -67.0, but it wasn't right...

    Please help...=]
     
  2. jcsd
  3. Nov 9, 2008 #2
    [tex]\textbf{f}=\Delta \textbf{p}/\Delta t[/tex].
     
  4. Nov 9, 2008 #3
    Ok the change in p would be...
    (.45kg)(3.2m/s)-(.45kg)(7m/s)???
    Im not really sure if i could just use the numbers from the problem or if i had to change the velocities or if they were in the correct order...
     
  5. Nov 9, 2008 #4
    [tex]\Delta \textbf{p} = m(\textbf{v}_f-\textbf{v}_i)/t[/tex], where the final velocity is 7 m/s in the negative direction and the initial velocity is 3.2 m/s in the positive direction.
     
  6. Nov 9, 2008 #5
    so it would be:
    .45kg(-7+3.2)/.047??
     
  7. Nov 9, 2008 #6
    Close.

    The final velocity is -7, the initial velocity is 3.2. But, the change in momentum is given by the change in velocity. Id est, final minus initial.
     
  8. Nov 9, 2008 #7
    Oh, so:
    .45kg(3.2-7)/.047??
     
  9. Nov 9, 2008 #8
    Final, -7, minus initial, +3.2, =>

    0.45kg (-7m/s - +3.2m/s)/0.047s =

    0.45kg (-10.2m/s) / 0.047s =...
     
  10. Nov 9, 2008 #9
    Wow. Thank you again. You are amazing...=]
     
  11. Nov 9, 2008 #10
    No big deal.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook




Loading...
Similar Threads for Momentum impulse volleyball Date
Impulse and momentum problem pool balls Saturday at 1:57 AM
Impulse and momentum question Friday at 10:17 PM
Impulse: multiple choice question Mar 6, 2018
How do we know how long the force is acting on an object? Feb 22, 2018
Sequental elastic and inelastic collisions Feb 6, 2018