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Homework Help: Raindrop Fall

  1. Mar 19, 2006 #1
    A raindrop has an initial downward speed of 10 m/s and its downward acceleration is given by
    [tex]a = \left \{ \begin{array}{cc} 9 - 0.9t, &0 \le t \le 10
    \\0, &t \ge 10\end{array}\right.[/tex]

    What is the velocity after 1s? (55 m/s)

    I did

    [tex]\frac{dv}{dt} = 9 - 09.t \Leftrightarrow v = 9t - 0.45t^2 + C[/tex]

    when
    [tex]t = 0, v = -10 = 9(0) - 0.45(0)^2 + C \Leftrightarrow C = -10[/tex]

    But with this I get -1.45.
     
    Last edited: Mar 19, 2006
  2. jcsd
  3. Mar 19, 2006 #2
    i think you got a mistype there...
    if you calculate the speed after 10s you should get 55 m/s.
    also notice the sign of C.
     
  4. Mar 19, 2006 #3
    Says 1 s in the book, so I guess it is a typo.
     
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