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    I'm really struggling with this question, and just need a bit of help. My understanding of the relationships between work-energy is poor so if someone could explain why some of it works, that would be great:

    A small model fire engine of mass 0.5kg is on a straight rigid plank, at angle z to the horizontal. It is projected up the plank along a line of greatest slope. Non gravitational resistance to motion is constant and has magnitude R newtons.

    When z =20, initial speed = 5m/s and comes to rest after moving 2 metres. Find R to 3s.f.

    I'm totally lost so any help or pointers would be really beneficial. Thanks!

    initial energy = sum of all final energies

    calculate work done by gravity, work done by friction, initial and final KE and put those into the above equation and you should be alright

    (Original post by toekneeofficial)
    alternatively, you must remember in a mechanical system, which is free to move, and to which the conservation of energy can be applied, positions of equilibrium occur when the potential energy has stationary values.
    if the potential energy has a minimum value then the equilibrium is stable and if the potential energy has a maximum value OR a point of inflexion, then the equilibrium is unstable.
    Dude, this is clearly irrelevant. Stop quoting word for word the passages from your mechanics book (yes I looked) in an attempt to show off your mechanics **** size, it's blatant and inappropriate.
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Updated: June 9, 2010
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