Oil is optically denser than water. When sound/light goes from optically denser medium to optically rarer medium, their velocity increase and they moves away for normal.
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The sound wave speeds up and bends

As, In optics we learnt that light undergoes refraction when travels from medium of different densities. Similarly, Sound also follows the law of refraction.
- It is due to the change of speed of water in different mediums, This makes it speed up or down depending upon the medium and their densities.
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C. when you can't achieve your goal due to events beyond your control
You don't need to worry about the 10 year bit with this question. Just grab a calculator and divide 100/2, then the answer to that (50) by 2 etc and keep dividing by 2 until you get down to 6.25.
The answer ends up being 4 half lives :)
If you don't understand what a half life is please let me know :)
The centripetal acceleration is given by

where v is the tangential speed and r the radius of the circular orbit.
For the car in this problem,

and r=40 m, so we can re-arrange the previous equation to find the velocity of the car: