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Calculate the velocity of the projectile

  1. Aug 28, 2009 #1
    1. The problem statement, all variables and given/known data
    A stone was thrown with initial velocity of 100 m/s. Calculate the velocity of the projectile at 10 m of height. (Consider g=10m/s^2, and neglect the effect of air molecules)


    2. Relevant equations

    where's the error in the following sollution?


    3. The attempt at a solution
    Vr= sqrt((Vx)^2+(Vy)^2)....(1) (Resultant velocity).
    Vx= Vi cos(a)....(2)
    Vy=Vi sin(a)+(-2gy)....(3)
    sub. (2)& (3) in (1)
    Vr = sqrt(Vi^2 (cos(a))^2+Vi^2 (sin(a))^2+(-2gy)); taking Vi as a common factor, and sqrt of both sides; we get
    Vr = sqrt(Vi^2-2gy) then we proceed by applying the given data from the problem
     
  2. jcsd
  3. Aug 28, 2009 #2

    kuruman

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    Re: Projectiles

    The error is right here

    Vy=Vi sin(a)+(-2gy)

    This equation is not dimensionally correct.
     
  4. Aug 29, 2009 #3
    Re: Projectiles

    Thanks Kuruman... so I believe it should be like this
    Vy^2= Vi^2 (sin(a))^2 - 2gy.
     
  5. Aug 29, 2009 #4

    kuruman

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    Re: Projectiles

    That's more like it.
     
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