SOLUTION: A man 1.8m tall walks ways from a lamp post 4m high at a speed of 1.5m/s. How fast in m/s does his shadow lengthen in m/s.

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Question 1149917: A man 1.8m tall walks ways from a lamp post 4m high at a speed of 1.5m/s. How fast in m/s does his shadow lengthen in m/s.
Answer by Boreal(15235) About Me  (Show Source):
You can put this solution on YOUR website!
Draw this as similar triangles
The height of the post is 4
the man is 1.8 m high to the right of the post.
The length of the horizontal leg from post to shadow tip is L
The shadow length is L-x
dx/dt, relative to the post is what we want
we also know that (L-x)/L=1.8/4=0.45
L-x=0.45L
x=0.55L
d/dt 0.55L=dx/dt; and dx/dt is 1.5 m/sec
dL/dt=1.5/0.55=
2.73 m/sec