# Word problem

• Mar 12th 2010, 03:47 PM
ascendancy523
Word problem
Here's my problem...

A street light is at the top of a http://webwork2.math.utah.edu/webwor...dd6e725061.png ft. tall pole. A man http://webwork2.math.utah.edu/webwor...5894998b41.png ft tall walks away from the pole with a speed of http://webwork2.math.utah.edu/webwor...7ba23575a1.png feet/sec along a straight path. How fast is the tip of his shadow moving away from the pole when the man is http://webwork2.math.utah.edu/webwor...c4e0d51871.png feet from the pole?

Any suggestions on how to start out?
• Mar 12th 2010, 04:33 PM
TKHunny
Absolutely! Draw some similar triangles. One has height of the flag pols. The other has height of the man.

Let's see what you get.
• Mar 12th 2010, 04:46 PM
ascendancy523
So I've drawn my similar triangles. I guess my question would be how do I relate the two to arrive at my answer. In other words, do I need to find the hypotenuse of the triangle with the height of the pole?
• Mar 12th 2010, 08:28 PM
TKHunny
Stuff we know...

x = the distance from the pole to the guy.

y = the length of the guy's shadow

p = height of pole

g = height of guy

Now, what do similar triangles do for us?

p/g = (x+y)/y
• Mar 13th 2010, 09:36 AM
ascendancy523
The ratio of their corresponding sides are similar.

so
x=44 ft
y=?
p=10.5ft
g=5.9ft

so to find y, plug in all the variables into the equation below? The problem is tough for me to comprehend because we're finding how fast his shadow is moving away from the pole but do we just assume the sun is in a certain location to give us the needed length of his shadow?
• Mar 13th 2010, 01:03 PM
TKHunny
You DO have to figure out that x = x(t) and y = y(t). The other two are constants.