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Calc problem (dY/d? triangle)

  1. Nov 19, 2005 #1
    i don't understand how to figure this problem out, and i really need the help.

    A kite is flying Y feet about the ground at the end of a 100 ft. string. the string makes an angle of ? (theta) with the ground.

    1. find the equation for dY/d?. what are its units?

    2. find dY/d? when Y= 50 feet. State the units

    3. if the angular velocite d?/dT =.8 radians per second, how fast is the kite rising when Y=50 feet?

    4. how fast is your answer to c in miles per hour?


    I AM COMPLETELY LOST, EXCEPT FOR I AM PRETTY SURE I CAN FIGURE OUT NUMBER 4 ONCE I HAVE THE ANSWER TO NUMBER 3 SINCE THIS HAS NOTHING TO DO WITH CALCULUS. PLEASE HELP ME........
     
  2. jcsd
  3. Nov 20, 2005 #2
    oops, all of those ?'s are actually supposed to be thetas, but the computer messed it up when i posted. please help me.
     
  4. Nov 20, 2005 #3
    OK, use pythagoras theorem and draw a diagram..
    100ft will be the hypotenuse (imagine it), Y is going to be, well, y... and using trigonometry you can express x in terms of the hypotenuse and theta...
    Form the equation with y = blabla with theta somewhere and then differentiate with respect to theta...
    For the question about what its units are, think of the derivative-- you're finding the rate of change of Y with respect to theta...... so given the unit of Y and the unit of theta, you can state the units as [unit of Y goes here] per [unit of theta goes here].
    For 3, you're going to be using the chain rule; by the looks of it, you're finding dy/dT
    4) Simple units conversion..

    Hope I helped out some? Someone correct me if I'm wrong somewhere, please!
     
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