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: Projectile motion (time cut in half)

  1. Mar 24, 2017 #1
    1. The problem statement, all variables and given/known data
    Two buildings A & B are each of height H as measured from the ground & are located a distance L apart. A tennis ball is shot horizontally with a velocity vo from building A such that it just hits the bottom of building B before hitting the ground. If building B is moved to half the distance (1/2)(L) & the ball is launched with the same horizontal velocity, where on building B does it hit the side, measured from the ground?

    2. Relevant equations
    I think they are:
    x-xo = (vocos(theta))t
    y-yo = (vosin(theta))t - 1/2(g)t2

    3. The attempt at a solution
    Where the ball would be at L/2 = x/2 & results in t/2 because x is proportional to time in the equation.
    So apply half the time to the y axis equation, but since it's 2 terms with different degrees of t (one is t1, the other t2) I'm not sure what I can assert about how this effects y.
  2. jcsd
  3. Mar 24, 2017 #2
    I just realized that the y axis won't use the equation I posted, the y axis is a one dimensional motion... I'll try this again
  4. Mar 24, 2017 #3
    Okay, is this correct:
    We can deduce that it'll be half the time from my reasoning in the first post.
    the y axis equation we need to use is: Δy = vot + ½at2
    since vo = 0, Δy = ½at2,
    if we apply t/2 we get Δy = ½a(½t)2 =(¼)½at2, so we'll end up with ¼*Δy, giving us 3/4H from the ground.

    Is this all sound reasoning?
  5. Mar 24, 2017 #4


    User Avatar
    Homework Helper
    Gold Member

    Looks good!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted