EK Optics questions

[Hexon]

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q917:
a certain animal swims at 4.0m/s.
if the animal takes the fastest path from its position on land to its home in the water and that path is shown below, how fast is the animal on land?

bird's eye view:

animal🙂
______ \
_______ \
30 degress\________________land
------------------------------
____________\60degrees______water
____________ \
_____________\
______________ \
_______________ home

choices:
a)2.0 m/s
b) 2.4 m/s
c) 6.8m/s
d) 8.0m/s

the answer says c, but i don't understand how you get that much. i got about 1.7 or so:S

 

[Liquidice07]

I don't understand the problem. Can you elaborate on the figure?

 

[MD Odyssey]

I suspect that this is a pseudo-Fermat's law type of problem. A better description might be useful.

 

[MShopes]

q917:
a certain animal swims at 4.0m/s.
if the animal takes the fastest path from its position on land to its home in the water and that path is shown below, how fast is the animal on land?

animal
\
\
30 \
------------------------------
\60
\
\
\
home

choices:
a)2.0 m/s
b) 2.4 m/s
c) 6.8m/s
d) 8.0m/s

the answer says c, but i don't understand how you get that much. i got about 1.7 or so:S

How is that an optics problem? I kept trying to figure that out for 5 minutes and still can't figure that out. It seems to be to be a velocity kinematics kind of problem.

But I still don't understand the problem....

 

[Hexon]

hey guys
yeah i tried drawing the picture which was a bird's eye view of an animanl running towards the water edge and into the water; they wanted to demonstrate diffraction;

i got the answer wrong and couldn't figure out the solution
i've redrawn the picture so it looks more distinct🙂

 

[paul411]

Still confusing. Scan/take a pic of the problem with your phone and post it.

Also post the correct answer and explanation.

 

[Hexon]

ah i figured it out😛 yeah, it was as one poster said, an application of fermat's theorem:
n=c/v and nsin(theta)=n2sin(theta2)

c/vsin(theta)=c/v2sin(theta2)

V1/V2=sin(theta)/sin(theta2).

so looking for V1 where V2=4m/s, sin(theta)=sin60, sin(theta2)=sin30
V1=6.8 which was the answer.

my problem was confusing which one was n1 v1 and which was n2 v2