C..............................
Answer:
Frequency is 
Explanation:
Distance between source 1 from the receiver , 
Distance between source 2 from the receiver , 
Now ,
Path difference , 
We know, for constructive interference path difference should be integral multiple of wavelength .
Therefore, 
It is given that n = 1,
Therefore, 
Frequency can be found by , 
Hence, this is the required solution.
Direction!
Velocity is a vector quantity and speed is a scalar quantity. Vector quantities includes both magnitude and direction, while scalar quantities only have magnitude. :)
The vector, the x-component and the y-component form a rectangle triangle where the vector is the hypothenuse and the x and y components are the two sides.
Calling

the angle between the vector and the horizontal direction (x), the two sides are related to

by

where vy and vx are the two components on the y- and x-axis. Using vx=10 and vy=3 we find

And so the angle is
Answer:
No sand doesn't stay sand forever.
Explanation:
- We may have a thought that the sand we see on the beach areas are always the same one for eternal, but it is not true.
- Due to different activities like beach nourishment, sand replenishment etc. the sand in the beach areas are changed and replaced.
- If the sand remained there for long time, it also affects the sand eating organisms and plants.