Answer:

Explanation:
A body has acceleration when there is a change in the velocity vector, either in magnitude or direction. In this case we only have a change in magnitude. The average acceleration represents the speed variation that takes place in a given time interval.
a)

b)

(10 waves) / (5 sec)
= (10/5) (wave/sec)
= 2 per sec
= 2 Hz .
Change in velocity = Final velocity - Initial velocity
Initial velocity = 20 m/s
Final velocity = 10 m/s
Change in velocity = 10 - 20 = -10m/s
Correct option B
Hope This Helps You!
Answer:
C. It speeds up, and the angle increases
Explanation:
We can answer by using the Snell's law:

where
are the refractive index of the first and second medium
is the angle of incidence (measured between the incident ray and the normal to the surface)
is the angle of refraction (measured between the refracted ray and the normal to the surface)
In this problem, light moves into a medium that has lower index of refraction, so

We can rewrite Snell's law as

and since

this means that

which implies

so, the angle increases.
Also, the speed of light in a medium is given by

where c is the speed of light and v the refractive index: we see that the speed is inversely proportional to n, therefore the lower the index of refraction, the higher the speed. So, in this problem, the light will speed up, since it moves into a medium with lower index of refraction.