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Help with 2 really easy assignments please

  1. Nov 28, 2006 #1
    Help with 2 really easy assignments please :)

    Hey there, fellas! I'm finnish so I probably don't know all the right terms (if any!), but I hope you get the point. So;

    An Audi A3 (mass 1205 kg) is overtaking a Volvo XC (mass 2113kg and velocity 40km/h) at 55 km/h

    a) Calculate the cars' motion energies
    b) On how big a hill would the Volvo have to drive to have as much potential energy as the Audi has motion energy?

    Here's the second one;

    A swimmer dives in the water from 10 metres. His mass is 85kg

    a) What's the biggest amount of potential energy he can get, errr.. "compared to the water". It's kinda hard to translate this one :/

    b) What is his speed on the moment he hits the water?

    c) at which height does the swimmer have 50% less velocity than in part b)?

    Hope the language isn't all that bad.. :/ Those two are really easy assignments for you I guess :)
  2. jcsd
  3. Nov 28, 2006 #2
    1a) Kinetic energy = (1/2)mv*v. Where m is the mass, and v is the velocity
    1b) kinetic energy = potential energy. (1/2)mv*v = (1/2)mgh. g is gravity, h is height (how high/big the hill is)

    2a) I think they want potential energy from the diving board to the ground.
    Like above. Potential energy = (1/2)mgh.

    2b) you want to find v_f. Where v_f is the final velocity. You know initial velocity = 0, because he is not moving at the start. You know acceleration = gravity. You should know some formulas to relate these.

    2c) Remember total kinetic energy + total potential energy = total energy for the whole thing. So they want 50% less velocity, which means 50% less velocity. Now that energy has to go somewhere. So it has to go into the potential energy. However much kinetic energy you lose, that is how much potential energy you must gain.

    Hope this helps.
  4. Nov 28, 2006 #3
    nevermind, need to check something
    Last edited: Nov 28, 2006
  5. Nov 28, 2006 #4
    For question 1b it does. I was not careful in specifying which kinetic energy and which potential energy (that is, which car). But I know G-nious is smart enough to figure it out.
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