When the distance between the source and the observer is DEcreasing, the observer sees light that has a<em> shorter wavelength</em> than the light actually had when it left the source.
It doesn't matter how the distance between them is decreasing. The source could be moving toward the observer, the observer could be moving toward the source, or they could both be moving in a way that makes the separation between them decrease as time goes on. The result is the same.
(When this is used in Astronomy and Astrophysics, the big trick is: How does the observer know what the wavelength actually WAS when the light left the source ?)
20 miles = 32186.9 meters
32186.9 / 340 = 94.667352
It will take 94.667 seconds to hear an explosion from 20 miles away.
Vector A is of magnitude 12 m and it makes an angle of 37 degree with Y axis
So here we can say that
Similarly we have
So here we have
option A is correct
3.
If the reaction forms a new substance it's a chemical reaction.