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: Bouncing Ball Problem, velocity vs. time

  1. Jun 10, 2010 #1
    This is my first college physics class and I am feeling a little challenged, since it is the start and all. I took physics in high school and am a bit rusty. I appreciate any help.

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

    The vertical component of the velocity of a bouncing ball is shown in the graph below (graph is very large). The positive Y direction is vertically up. The ball deforms slightly when it is in contact with the ground.

    [PLAIN]http://img180.imageshack.us/img180/494/graphz.png [Broken]

    They want for part a: Identify the instances in time where the ball is at maximum height.

    2. Relevant equations

    None really for part a. Part b asks you to calculate the average velocity while the ball is in the air. Part c, when it is on the ground. Part d asks for the maximum height above the floor using the area under the graph. So for parts b and c I guess you have to use a = v / t. I will probably need some help with these. I will continue the thread when I finish part a.

    3. The attempt at a solution

    I am kind of mixed up on where to start for part a. I do know the vector direction is negative where the line slopes are negative, and positive respectively. At this point I am assuming that the ball is falling when the function is below the x axis and rising when it is above the x axis.
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Jun 10, 2010 #2
    You're correct in that the ball is falling when the function is below the x axis

    Think about what the gradient of a line at any point on the graph represents, and how this is affecting the velocity.

    When the ball is at maximum height, what would the velocity at that point be?
  4. Jun 10, 2010 #3
    So, maximum height is denoted by when the the function crosses zero?
  5. Jun 10, 2010 #4
    That's only half correct, its not every time the function crosses zero
  6. Jun 10, 2010 #5
    So does the ball hitting the floor happen at 1.125 seconds, 3.875 seconds?

    Max Height 0 seconds, 2.25 seconds, and 5 seconds?
  7. Jun 10, 2010 #6
  8. Jun 10, 2010 #7


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    The ball has no velocity at t=1.125 and t= 3.375 seconds (you misread the graph on that last figure), but the ball hits the floor at 9m/s, when t=? and ?
  9. Jun 10, 2010 #8
    Ahh yes, I was wrong with respect to that, my apologies

    I was focusing too much on maximum height, and missed that error
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook