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Two Related Rate Problems?

First, a cylindrical tank with radius 5 meters is being filled with water at a rate of 3 m^3/sec. How fast is the height of the water increasing?

Second, Two cars start moving from the same point. One travels south at 60 mi/h and the other travels west at 25 mi/h. At what rate is the distance between the cars increasing two hours later?

Help on either of the two is greatly appreciated! Please show work if you can.

4 Answers

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  • 1 decade ago
    Favorite Answer

    r = 5

    dV/dt = 3

    V = π r² * h

    V = 25π * h

    dV/dt = 25π * dh/dt

    dh/dt = (dV/dt) / 25π

    dh/dt = 3 / (25π)

    dh/dt = 0.0382

    Height of water is increasing at rate of 0.0382 m/sec

    --------------------

    Let x be position of first car from start point

    Let y be position of second car from start point

    Let t be the time in hours

    x = 60t . . . . . . dx/dt = 60

    y = 25t . . . . . . dy/dt = 25

    Let s be distance between the two cars

    s² = x² + y²

    At time t = 2 hours,

    x = 120

    y = 50

    s² = 14400 + 2500 = 16900

    s = 130

    Differentiate with respect to t:

    s² = x² + y²

    2s ds/dt = 2x dx/dt + 2y dy/dt

    s ds/dt = x dx/dt + y dy/dt

    130 ds/dt = 120*60 + 50*25

    130 ds/dt = 8450

    ds/dt = 8450/130

    ds/dt = 65

    Distance between cars is increasing at a rate of 65 miles/hour

  • 1 decade ago

    r = 5

    V = pi*r^2*h = pi*5^2*h = 25*pi*h

    Therefore, dV/dh = 25*pi

    dV/dt = 3

    By the Chain Rule:

    dV/dt = dV/dh * dh/dt

    3 = 25*pi * dh/dt

    3/(25pi) = dh/dt

    dh/dt =~ 0.038 meters per second

    dh/dt =~ 38 mm per second

    After t hours, first car is 60t miles south, and second car is 25t miles west

    By Pythagoras, if the distance between them distance between them is d, we have:

    d^2 = (25t)^2 + (60t)^2

    d^2 = 625t^2 + 3600t^2

    d^2 = 4225t^2

    d = 65t

    Rate of change of d (with respect to t):

    dd/dt = 65

  • DWRead
    Lv 7
    1 decade ago

    volume = πr²h

    = 25πh m³

    After 1 second the tank contains 3 m³.

    3 = 25πh

    h ≅ 0.038 m

    The height is increasing at 0.038 m/sec.

  • fodor
    Lv 4
    4 years ago

    a million. something is incorrect with this question. factor (5, -2) isn't on graph of x³y² = 200 (5,-2) is positioned on graph of x³y² = 500 (2,-5) is positioned on graph of x³y² = 200 Please verify question, and let us know in case you typed it in incorrect, or if the errors is on your e book. besides, to verify this subject, you may desire to differentiate implicitly with appreciate to time (t in minutes) 3x²y² dx/dt + 2x³y dy/dt = 0 Now replace x with it proper fee (5?) and y with its proper fee(-2?), and dx/dt with -4. Use those values to calculate dy/dt. it is your answer. be conscious: If equation of graph isn't x³y² = 200, then this could exchange results of by-product (until the only distinction is the consistent on top area) ______________________________ 2. obtainable crate: 4 thousand value in line with crate: $25 furnish changing at value of -0.3 thousand/day x = 4 p = 25 dx/dt = -0.3 px + 7x + 8p = 328 Differentiate with appreciate to time (t) x dp/dt + p dx/dt + 7 dx/dt + 8 dp/dt = 0 (x + 8) dp/dt + (p + 7) dx/dt = 0 (4 + 8) dp/dt + (25 + 7) (-0.3) = 0 12 dp/dt - 9.6 = 0 12 dp/dt = 9.6 dp/dt = 0.8 value is increasing at a value of $0.80 (80 cents) in line with day M?thm?m

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