11@Ashish-the answer to the first question is 12m..
Use the critical angle concept..
1. A bulb is placed at a depth of 2√7m in water and a floating opaque disc is placed over the bulb so that the bulb is not visible from the surface. What is the minimum diameter of the disc?
2. A fish rising vertically to the surface of a lake at 3m/s observes a bird diving vertically at the rate 9m/s. Find the actual velocity of the bird.
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4 Answers
11
1well i did not get it by that method....i was getting some bad answer
11
From snell's law-:
μ1sinθ1=μ2sinθ2
where θ2=90°,μ2μ1=34 and θ1=x
sin x=34 or x=sin-134
in the triangle ABC
tan x=r2√7
or r=tanx*2√7
r=tan(sin-134)*2√7
after simplifying it we get r=6m..
So the least diameter=2r=2*6=12m
