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!

Motion in 2 Dimensions

  1. Feb 22, 2009 #1
    1. The problem statement, all variables and given/known data
    A brick is thrown upward from the top of a building at an angle of 25 degrees to the horizontal. It's initial speed is 15 m / s. If the brick is in flight for 3 seconds, how tall is the building? Thanks for the help.


    2. Relevant equations



    3. The attempt at a solution
    i thought i could use delta y = (Vo*sin*25 degrees)t - 1/2gt^2
    but when i plugged everything in i got 63.1m, which is different from my friends 25m. I thought i could use this equation because it seems i have every piece of it and i just needed to plug it in. Did i just find how high the brick was from the ground? I don't know how to find the height of building...i'm confused
     
    Last edited: Feb 22, 2009
  2. jcsd
  3. Feb 22, 2009 #2

    PhanthomJay

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Your equation is good! Your math is not so good. Recheck your numbers.
     
  4. Feb 22, 2009 #3
    i still cannot find out what i am doing wrong. My Vo is 15m/s, sin*25 degrees, time is 3 sec, g is -9.8m/s^2

    i get the same answer

    Whoops...i had g=-9.8, and it had to be a positive in order for this to work.

    Thank you!
     
    Last edited: Feb 22, 2009
  5. Feb 22, 2009 #4

    PhanthomJay

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    You are getting mixed up on your plus and minus signs. If up is positive, then down is negative. I thought you had already built your minus sign into the equation, which should read [tex]y = v_{yi}t +1/2(g)t^2[/tex]. Then plug in g =-9.8. and y comes out to -25, indicating the displacement after 3 seconds is 25 m downward from the top of the building.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Motion in 2 Dimensions
  1. Motion in 2 dimensions (Replies: 1)

Loading...