Optics Question 802
Question: A ball is dropped from a height of 20 m above the surface of water in a lake. The refractive index of water is 4.3. A fish inside the lake, in the line of fall of the ball, is looking at the ball. At an instant, when the ball is 12.8 m above the water surface, the fish sees the speed of ball as $ [Takeg=10m/s^{2}] $
Options:
A) 9m/s
B) 12m/s
C) 16m/s
D) 21.33 m/s
Show Answer
Answer:
Correct Answer: C
Solution:
[c] Consider the activity A to B Applying $ v^{2}-u^{2}=2as $
$ v^{2}-0^{2}=2\times 10\times 7.2 $
$ \Rightarrow v=12m/s $
The velocity of ball as perceived by fish is $ v’{= _{w}}\mu \times v=\frac{4}{3}\times 12=16m/s $
