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Homework Help: Projectile Problem

  1. Feb 24, 2012 #1
    1. The problem statement, all variables and given/known data

    http://u.spig.in/forum/105599049.jpg [Broken]

    A projectile is fired at t=0 with velocity v = 20√2 m/s at an angle of 45° degrees as shown. A wall inclined at the same angle and at a distance of 40 m starts moving towards the projectile at the same time (ie., t=0) with a speed of 20m/s. Find the time at which the ball collides with the the wall.

    2. Relevant equations

    General Kinematical Equations

    3. The attempt at a solution

    I'm getting answer as 2(√3-1) s. Strikingly this is very similar to my friend's answer i.e, 2(√2-1) s. I don't know whose one is correct. Help me.

    My Solution,

    Let the base of the wall has moved a distance 40-x m at the time the ball collides with the wall. Let the height at which the collision occurs is y.
    Then we have,
    20t = 40-x ..... (1) (for wall)
    y = 20t-5t2 ...... (2) (for ball)
    and x+y=20t ..... (3) (General diagram and since angle is 45 deg)

    Solving for ' t ' , a quadratic I got, t = 2(√3-1) s (Other value being negative)
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Feb 24, 2012 #2
    I get your answer.
     
  4. Feb 25, 2012 #3
    Thanks for verifying.
     
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