math

At noon, ship A is 30 nautical miles due west of ship B. Ship A is sailing west at 21 knots and ship B is sailing north at 15 knots. How fast (in knots) is the distance between the ships changing at 4 PM? (Note: 1 knot is a speed of 1 nautical mile per hour.)


this is a cal problem.

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asked by lisa
  1. after 4 hours
    x = - 30 - 21*4 = - 114
    y = 15*4 = 60
    dx/dt = -21
    dy/dt = 15

    D at 4 hr = sqrt(114^2+60^2) = 129
    D^2 = x^2 + y^2
    2 D dD/dt = 2 x dx/dt + 2 y dy/dt
    129 dD/dt = -114(-21) + 60(15)
    dD/dt = 25.5 knots

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    posted by Damon
  2. i think ur answer is wrong

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    posted by lisa
  3. I got the same answer as Damon.
    Damon is right.

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    posted by Reiny
  4. i type it in the computer , its says its wrong. but thanks

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    posted by lisa

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