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Projectile motion

  1. Oct 20, 2009 #1
    1. The problem statement, all variables and given/known data
    A ball is projected horizontally from the top oF A CLIFF WOTH SPEED U. iF AIR RESISTANCE IS NEGLECTED AND G IS ASSUMED to be 10 ms-2, the velocity of the ball is found to be 50ms-2, 3 seconds later. What is the value of u


    2. Relevant equations
    s=ut+1/2at2
    s=vt
    v2=u2+2as
    v=u+at

    3. The attempt at a solution
    well the problem is i do not know to use which components either x or y
    if i use x, but in projectile motion and newton 1st law, the speed of x will not change as there is no other force to push or pull the ball
    however, usually we use the initial speed for x only, and for y is 0
    so how X.X
     
    Last edited: Oct 20, 2009
  2. jcsd
  3. Oct 21, 2009 #2
    well no1 can solve it ? ==
     
  4. Oct 21, 2009 #3

    rl.bhat

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    Homework Helper

    Ball moves horizontally without any change in its velocity U
    Ball falls vertically withe zero initial velocity.
    What is its velocity V in the vertical direction after 3 seconds?
    U and v are perpendicular to each other.
    What is the resultant of these two velocities?
    Equate this resultant velocity to 50 ms^-1. , and find U
     
  5. Oct 21, 2009 #4
    well this is what i have done
    v=u+at
    v=0+(9.8)x(3)
    v=[tex]\frac{147}{5}[/tex]
    using Pythagorus theorem,
    a2+b2=c2
    ([tex]\frac{147}{5}[/tex])2+b2=502
    so the b=40.44
    yep i got the answer thx so much
     
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