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Trouble with mechanical physics

  1. Dec 10, 2008 #1
    A 70 kg trampoline artist jumps vertically upward from the top of a platform with a speed of 4.5 m/s. (Ignore small changes in gravitational potential energy.

    (a) How fast is he going as he lands on the trampoline, 3.0 m below?
    (b) If the trampoline behaves like a spring with spring stiffness constant 5.2 multiplied by 104 N/m, how far does he depress it?

    I think i have to use kinematics but I don't really know how to execute it

    A 1400 kg sports car accelerates from rest to 80 km/h in 7.4 s. What is the average power delivered by the engine?
    I put 112000 W but it is wrong and I don't know what to do to get it write

    please help me with one or both of these that would be great
  2. jcsd
  3. Dec 10, 2008 #2


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    Gold Member

    For part (a), think about the conservation of mechanical energy. ([tex]E=\frac{mv^2}{2}+mgh[/tex]).

    For part (b), use Hook's law. (Check out wikipedia or google it).
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