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Homework Help: Help! Work, Energy and Power!

  1. Jan 18, 2012 #1
    I have some examples of physics i dont quite understand, so please if you could explain me how to solve them and what to do.
    1. Object of mass 2kg starts to fall from height 10m,count his kinetic energy when it passes from point which is on height 2m.
    2. Object of a mass 2kg is thrown from surface of earth with beginning speed 20m/s
    a) what is his speed on height of 5meters
    b) whats his kinetic energy on height of 10meters
    c) whats his maximum he can get.
    3.Object starts to fall from height of 100 meters, on which height his kinetic energy will be 2/3 potencial energy.
    4. Mass of a object is 500 grams, speed is 72km/h, 10 meters of height, determine power.
    5.Power of object 0,4kW performed work of 1600J determine time.
    6.Force of 20N performs work if 120J on angle 45 degrees. Determine distance which passed (i think) if its something else which you think needs to be solved in 6 example explain me that way.
    On 1. example i tried to solve it, like count potential energys of both heights than substract it...idk if thats right
    2. a) and c) i understand a little.. but i dont know b)
    3. i divided 100 by 3, than multiplied by 2...but it think this is wrong way
    4.i cant find formula for this i tried but i dont know if i calculated good
    5. i used formula t=A/P is it right formula?
    6.im not sure what does it need to calculate with that i guess passed distance, i tried to calculate it and turned out 3V2 is it right?
    Last edited: Jan 18, 2012
  2. jcsd
  3. Jan 18, 2012 #2


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    Homework Helper

    1) yes. mg(8m)
    2) KE(1) + PE(1) = KE(2) + PE(2) ... 1 and 2 are different places
    3) yes.
    4) what specifically did you do? Power by what? (gravity?)
    5) (Power = Work/time ... what do you mean by "A"?)
    6) Work = F dot distance ... dot means parallel component (cos theta)
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