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Math Help - which Equations constant I use here ?

  1. #1
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    which Equations constant I use here ?

    Hi ALL

    which Equations constant I use here ?

    a truck covers a distance of 50 m in 8 s while smoothly sowing down to a final speed of 2.5 m/s . find its original speed

    Dx = 50 m
    t = 8 s
    v = 2.5 m/s

    Now I take this equation bit I don't now why I didn't get the correct answer


    Dx = (v + v0 ) t/2

    =50 = 2.5 + v0 ) 8 /2
    =2 X 50 + 92.5 + v0 ) 8 /2
    =100 = 20 + 8v0/2
    =128v
    v = -128
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  2. #2
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    but here in my book the answe is 10 m/s
    ??

    they do v0 = 2DX/2-v = 2 X 50 /8 -2.5 = 10
    ??please I want the help beacuse I fell confused
    I wait
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  3. #3
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    skeeter's Avatar
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    sorry ... forgot the 8 seconds

    50 = \frac{1}{2}(v_0 + 2.5) \cdot 8

    50 = 4(v_0 + 2.5)

    \frac{25}{2} = v_0 + 2.5

    v_0 = 10
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