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!

A ball is thrown from the roof of a building

  1. Dec 6, 2005 #1
    It is s(t)=245+24.5t-4.9t(sqrd) meters from the ground (t) after it is thrown. s(t) = displacement function that describes the position of the ball from the ground at time t.

    Determine height of building, time it takes the ball to reach the ground and the velocity when it hits the ground.

    I've been messing around with first, second derivatives and breaking down the original equation into t=10 and t=-5 but I don't know where to go from here.

    Help apperciated.

    i should mention i took physics 2 years ago and dont remember much of it
    Last edited: Dec 6, 2005
  2. jcsd
  3. Dec 6, 2005 #2


    User Avatar
    Gold Member

    Well since the idea of negative time here is worthless, how could you use that t=10?
  4. Dec 6, 2005 #3
    Well I plug it in the equation and get 980???
  5. Dec 6, 2005 #4


    User Avatar
    Gold Member

    What equation did you put t=10 into?
  6. Dec 6, 2005 #5
  7. Dec 6, 2005 #6


    User Avatar
    Gold Member

    Recalculate that. What do you think the position will be after 10 seconds?

    You wouldn't think that after 10 seconds, the object is 980 meters off the ground...
  8. Dec 6, 2005 #7
    Of course I woudn't that's why it doesn't make any sense to me.
    I think im fundementally not getting some kind of simple concept here.
    1st derivative when 10 is plugged in i get 1.47
  9. Dec 6, 2005 #8


    User Avatar
    Gold Member

    Well you were doing the calculation wrong.

    245 + 24.5(10)-(4.9)(10)(10)=0 which is the position at t=10.

    What equation do you use for finding the velocity in the y direction?
  10. Dec 6, 2005 #9
    v(t)=s dirvative(t)

    I don't know. I'm not taking physics. I've covered my calculus books chapter and coudnt find anything.

    I'm gonna rest on it, thanks for you help though.
  11. Dec 6, 2005 #10


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Where is the ball at t=0?

    At what time does s(t) = 0 and where is the ball then?

    How do you find the function which discribes the velocity as a function of time?
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: A ball is thrown from the roof of a building
  1. Rock thrown from roof (Replies: 3)