A man is 2 m tall is walking at a rate of 1 m per second in a straight line away from a 10 m lamppost. How fast is the tip of his shadow moving away from the lamppost?

Answer 1

If his distance from the pole is x and the length of the shadow is s, then

s/2 = (s+x)/10
1/2 ds/dt = 1/10 (ds/dt + dx/dt)
4 ds/dt = dx/dt

So, the length of the shadow is growing 1/4 as fast as the man's speed.

But that's not how fast the tip of the shadow is moving. You can figure that out, I think.

Answer 2

i am not getting the point,can you elaborate more