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Math Help - Need help :( I dun understand

  1. #1
    Junior Member
    Joined
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    Singapore
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    Need help :( I dun understand

    Hi guys,

    Pls refer to the attachment.

    I dun understand the following,
    a) For the Damping Force, R1, why is it ''i'' but not ''-i''?
    b) For the Damping Force, R2, why is it ''-i'' but not ''i''?
    b) For the Spring Force, H, why is it ''i'' and not ''-i''?
    c) Lastly, for Spring Force, H, why is it -k(x - lo)i?

    Please explain to me in simple english, i asked my lecturer but i still don't understand

    Rgds,
    WeiJing
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  2. #2
    MHF Contributor

    Joined
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    Re: Need help :( I dun understand

    The "damping force" is proportional to the velocity and always opposes it. The crucial point is NOT that R1 is "i" or "-i" but that it is "-x' i". It is horizontal, so "i" and it is opposite to the velocity, x', so -x' i. Similarly, R2 is opposite to the speed relative to position "B" which is x'- y'. "H" is the spring force. If the spring is compressed, that is if x is less than l_0, the force tends to "uncompress" and if the spring is stretched, that is if x is larger than [tex]l_0[tex] the force tends to "unstretch". In either case it is opposite to x- l_0 so proportional to -(x- l_0)= l_0- x
    Thanks from wasp and weijing85
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