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: Stumped on long problem

  1. Oct 16, 2008 #1
    1. The problem statement, all variables and given/known data

    I need someone to walk me through this problem. I know its a bit lengthy, but my teacher hasn't explained how to do this, and I'm completely stumped.

    A ball of mass 0.6 kg, initially at rest, is
    kicked directly toward a fence from a point
    20 m away, as shown below.
    The velocity of the ball as it leaves the
    kicker’s foot is 18 m/s at angle of 62 ◦ above
    the horizontal. The top of the fence is 9 m
    high. The kicker’s foot is in contact with the
    ball for 0.06 s. The ball hits nothing while in
    flight and air resistance is negligible.
    The acceleration due to gravity is 9.8 m/s2.

    Determine the time it takes for the ball to
    reach the plane of the fence. Answer in units
    of s.

    Hint: Consider the diameter of the ball to be
    How far above the top of fence will the ball
    pass? Answer in units of m.

    What is the vertical component of the velocity
    when the ball reaches the plane of the fence?
    Answer in units of m/s.

    2. Relevant equations

    No clue...

    3. The attempt at a solution

    My teacher just randomly decided to give us this, even though we haven't learned it. And I'm not exaggerating, and therefore I'm completely lost.
  2. jcsd
  3. Oct 16, 2008 #2
    haha poor you with this teacher :(

    to reach the plane of the fence you need to find the time (in seconds) to travel the necessary horizontal distance
  4. Oct 16, 2008 #3
    Can I just get an answer please? I have no idea how to do this. I would really like to go to bed. I'll try and figure out the problem tomorrow. I know you are trying to help me, and I appreciate it. It's just been a very tiring day, and I have to get up early tomorrow again.

    Thank you.
  5. Oct 16, 2008 #4


    User Avatar
    Homework Helper

    OK. You can do it anyway.

    What are the x,y components of velocity. (Hint: 62 degrees)

    Knowing the y velocity what is the equation for y position as a function of time?
    Likewise for x.

    With the x,y functions of position as a function of time you can figure out the rest.

    Need formulas?
  6. Oct 16, 2008 #5


    User Avatar
    Homework Helper


    You can do it if you put in the effort. People will help if you get stuck.

    Sorry but forum rules are no effort = no answers.
  7. Oct 16, 2008 #6
    err...2.37 seconds until the ball reaches the fence? correct?
  8. Oct 16, 2008 #7
    sounds good to me
  9. Oct 16, 2008 #8
    What about the rest? I'm really confused on the magnitude part.
  10. Oct 16, 2008 #9
    ill get back to you asap
    for now i need to go to my Dynamics class

    good luck
    if u need sleep go get it.. u will think better when you are rested :)
  11. Oct 16, 2008 #10
    It's due tomorrow, 6 AM, its an online hw.
  12. Oct 16, 2008 #11
    And I missed a question:
    Determine the magnitude of the average
    net force exerted on the ball during the kick.
    Answer in units of N.
  13. Oct 16, 2008 #12
    I got the ball being 35 m above the goal/gate/whatever? Confirm/reject?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook