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Math Help - speed velocity

  1. #1
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    speed velocity

    A person is traveling 650 fpm it takes them 25 seconds to stop how many feet did it take?
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  2. #2
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by dmark View Post
    A person is traveling 650 fpm it takes them 25 seconds to stop how many feet did it take?
    First convert your units.

    650 fpm = 650 ft/min = 650 ft/(60 s) = 10.83333 ft/s

    d = vt

    d = (10.83333 ft/s)(25 s) = 270.8333333 ft

    Or 271 ft.

    -Dan
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  3. #3
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    Thank you

    Thank you for your answer. In this problem it is not a constant volocity but a deceling. Do I need to use the slope? y=ax+b?
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  4. #4
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by dmark View Post
    Thank you for your answer. In this problem it is not a constant volocity but a deceling. Do I need to use the slope? y=ax+b?
    I hate it when I do that! My apologies!

    Quote Originally Posted by dmark View Post
    A person is traveling 650 fpm it takes them 25 seconds to stop how many feet did it take?
    Let's try this again:

    We don't know the acceleration so let's use an equation that doesn't involve the acceleration:
    x = x0 + (1/2)(v0 + v)t

    I'm envisioning a coordinate system where + x is in the direction of motion and the origin is at where the person starts to decelerate. Thus x0 = 0 ft, v0 = 650 ft/min, v = 0 ft/min. Using the unit conversion from my first post we get that
    v0 = 10.833333 ft/s.

    Thus:
    x = (1/2)(v0)t = (1/2)(10.833333 ft/s)(25 s) = 135.417 ft

    So 135 ft.

    -Dan
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