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Homework Help: Ball thrown up with an initial speed of 27.0 m/s

  1. Oct 21, 2008 #1
    1. The problem statement, all variables and given/known data
    A) The ball's PE is a constant.
    B) The velocity vector and the acceleration vector are in the same direction after t= 7.3s.
    C) The acceleration is constant.
    D) The acceleration is 0 near t= 7.3s.
    E) Maximum height is reached at about t=7.3s.
    F) The ball's KE increases during the first second.

    3. The attempt at a solution
    I am pretty sure of the following. Somewhere i am wrong.
    A is false
    B is true (given once it hits 7.3, gravity is negative(acceleration) and the direction is necative
    C is true because accel is gravity and that is always constant.
    D is false because if the gravity is constant than it wouldnt be zero
    E is true because it starts coming down after 7.3 s
    F is true because KE is zero when the ball is in hand but when he releases it, it gains
     

    Attached Files:

  2. jcsd
  3. Oct 21, 2008 #2
    I can't see the image until it's approved, but this is my input

    A - I would agree that this is false.
    B - mathematically I would agree, however I would say that the ball has long since hit the ground at this point. (possibly numbers are wrong)
    C - I would agree that this is true.
    D - I agree that this is false.
    E - I would disagree here, how did you come to this conclusion? It looks more like 2.75 seconds to me. Unless you've stated some of the numbers wrong/I've misinterpreted them.
    F - kinetic energy of course being: .5mv^2 Think about which way the ball is accelerating, think of if v is increasing or decreasing.

    EDIT: latex isn't working for me
     
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