Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Related rates, help please

  1. Nov 16, 2005 #1
    An object is dropped from rest from a height of 200 ft, 300 feet horizontally across from a 200 ft tall light tower. The object's height above the ground at any given time, t, in seconds, is h= 200 - 16t^2 feet. Exactly 2 seconds after it is dropped, what is the rate at which the shadow is moving across the ground???
  2. jcsd
  3. Nov 16, 2005 #2
    i don't even know what to start with, any suggestions?
  4. Nov 17, 2005 #3


    User Avatar
    Science Advisor

    Yes- start by drawing a picture. Draw a vertical line representing the light tower and a horizontal line representing the ground. Mark a point representing the falling object. Draw a straight line from the top of the light tower through the object to the ground. The point where that line touches the ground is the shadow of the object. Finally draw a vertical line from the object to the ground. Now look at it!

    You should see two similar triangles so you can set up an equation involving information you know and the distance from the light tower to the shadow. Differentiate that distance with respect to time to get the rate at which it is moving.
  5. Nov 19, 2005 #4
    ill try that
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook