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Homework Help: Force and free fall

  1. Mar 15, 2005 #1
    Can anyone help me with any of these 3 questions?

    1. Wrongly called for a foul, any angry basketball player throws the ball straight down to the floor. If the ball bounces straight up and returns to the floor 2.5s after first striking it, what was the ball's greatst height above the floor?

    (ok, so I know that its a symmetrical motion but I don't think I can do anything unless I can get either an initial or final velocity...any suggestions?)

    2. Standing side by side, you and a friend step off a bridge at different times and fall for 1.6s to the water below. your friend goes first and you follow after he has dropped a distance of 2m. When your friend hits the water, what is the distance of separation between you two?

    (I'm confused with the concepts of this Q and how to approach it...can anyone give me a few tips or so?)

    3. The force of water resistance on a swiming whale can be approsimated by F = bv where v is the swiming speed, b is a constant with units N x s/m. Find the maximum speed of the whale, assuming it can produce a power P?
    (Ans: root(p/b))

    (With this Q, I just thought F/b will give v...but how come there's a root in there?)

  2. jcsd
  3. Mar 15, 2005 #2

    Chi Meson

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    Shouldn't this thread be in the homework help zone?

    Here's a start on question 1: Think about the time needed to get to the highest point as compared to the toatl time in the air. Now think about the ball's instantaneous velocity at the highest point.

    #2: How much time goes by before you jump? This will be the same amount of time between splashes. 1.6 s minus this time = how long you were in the air when your friend splashes.

    # 3 : P = W/t = (Fd)/t = F (d/t) = Fv

    Go from there?
  4. Mar 19, 2005 #3
    For question 2 :
    Think about a mass m falling for 1.6 seconds with an acceleration of g. This should give you an idea of the total distance of the fall

    Then you can look in you text for the equation that gives you x(t) (position as a function of time) relating to g.
    After the first friend falls for 2 meters, he will have fallen for a time t. Subtracting this time t from 1.6, you get how long the second friend can fall before the first person hits the water. Using this information, you should be able to find the distance of the second friend to the water
  5. Mar 19, 2005 #4
    For #1:
    Conservation of energy will probably be your best bet here, realize the ball makes a symmetric jump and fall in 2.5s, so you should be able to decipher the time when it reaches the top. At the peak of the fall you should know its velocity is 0, and from there it is a simple freefall problem.
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