Results 1 to 2 of 2

Math Help - Related rates problem

  1. #1
    Junior Member
    Joined
    Jul 2007
    Posts
    45

    Related rates problem

    Hello, I'm working on a related rates problem that I can't seem to get. It should be fairly easy, but trying to piece the values together just isn't working out for me.

    The question is:
    A railroad bridge is 20 m above, and at right angles to, a river. A person in a train travelling at 60 km/h passes over the centre of the bridge at the same instant that a person in a motorboat travelling at 20 km/h passes under the centre of the bridge. How fast are the two people separating 10 seconds later?

    Thank you in advance for any help!
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Eater of Worlds
    galactus's Avatar
    Joined
    Jul 2006
    From
    Chaneysville, PA
    Posts
    3,001
    Thanks
    1
    This is done like other Pythagoras related rates problems, only you have a 3-dimensional component.

    D^{2}=x^{2}+y^{2}+20^{2}

    Differentiate:

    D\frac{dD}{dt}=x\frac{dx}{dt}+y\frac{dy}{dt}

    Now, you have dx/dt, dy/dt, and you can find D once you know x and y. Find x and y after each has traveled 10 seconds. For instance, at 60 km/h, how far does the boat travel in 10 seconds. That could be your x. Carry on?.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Related rates problem
    Posted in the Calculus Forum
    Replies: 1
    Last Post: November 16th 2011, 10:30 AM
  2. related rates problem
    Posted in the Calculus Forum
    Replies: 3
    Last Post: October 22nd 2009, 04:11 PM
  3. Related rates problem
    Posted in the Calculus Forum
    Replies: 1
    Last Post: October 3rd 2009, 03:42 PM
  4. Related rates problem..see pic
    Posted in the Calculus Forum
    Replies: 1
    Last Post: April 20th 2009, 10:05 AM
  5. Another related rates problem
    Posted in the Calculus Forum
    Replies: 9
    Last Post: December 7th 2008, 05:55 PM

Search Tags


/mathhelpforum @mathhelpforum