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Homework Help: Golf ball vector problem

  1. Sep 26, 2004 #1
    A golf ball is hit off a tee at the edge of a cliff. Its x and y coordinates as functions of time are given by the following expressions.

    x = (15.0 m/s)t

    y = (2.00 m/s)t - (4.90 m/s2)t2

    (a) Write a vector expression for the ball's position as a function of time, using the unit vectors i and j. (Use t, i and j as necessary.)
     
  2. jcsd
  3. Sep 26, 2004 #2
    You have all the information you need. v = a*i+b*j where i is the x direction and j is the y direction. a and b specify the magnitude of the i and j directions, respectively. I am not sure how to answer this question without just flat out telling you.

    Say you have the cartesian point (3,4)

    in vector form this is 3i+4j
     
  4. Sep 26, 2004 #3
    yeah lol, got that one and the next couple, but having trouble with the next few:
    (a) Write a vector expression for the ball's position as a function of time, using the unit vectors i and j. (Use t, i and j as necessary.) Got this one
    r = correct check mark m
    (b) By taking derivatives, obtain an expression for the velocity vector v as a function of time. Got this one
    v = correct check mark m/s
    (c) By taking derivatives, obtain an expression for the acceleration vector a as a function of time. Got this one
    a = correct check mark m/s2

    Don't get these :
    (d) Next use unit vector notation to write an expression for the position of the golf ball at t = 1.20 s.
    r(1.20 s) = ( m ) i + ( m ) j
    (e) Write an expression for the velocity at this time.
    v(1.20 s) = ( m/s ) i + ( m/s ) j
    (f) Write an expression for the acceleration at this time.
    a(1.20 s) = ( m/s2 ) j
     
  5. Sep 26, 2004 #4
    lol nevermind, got them all
     
  6. Sep 26, 2004 #5
    I think semantics are messing you up. All they're asking is using the formulae you derived, plug t = 1.20s into each of them: position for d, velocity for e and acceleration for f. Your previous equations should have told you what the i and j components will be at any time t.
     
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