Mr. Simon, who is 6 feet tall, walks a rate of 4 feet per second away from a light that is 13 feet above the ground. Find the rate at which his shadow’s length is changing when he is 10 feet from the base of the light.

Question

Mr. Simon, who is 6 feet tall, walks a rate of 4 feet per second away from a light that is 13 feet above the ground.  Find the rate at which his shadow’s length is changing when he is 10 feet from the base of the light.

btaylor · Answer

I love this type of question. 
The first step in all related-rates problems like this is to draw a picture.

btaylor · Answer

|dw:1394308624644:dw|
Instead of looking at this as the rate of change of the angle (absolutely miserable, let me assure you), look at it as two similar triangles. Can you set up a proportion based on the similar triangles?

btaylor · Answer

Once you set up the proportion, differentiate with respect to time (d/dt). You know the rate at which d is changing, so you should be able to plug in what you know and find ds/dt at d=10.

turingtest · Answer

@syamiza92 please try to respond to @BTaylor 's questions so he can help you. If you remain silent, nobody knows where exactly you need help.

anonymous · Answer

sorry, i just trying to do other question.. thanks by the way.. already got it