When light moves from a medium with higher refractive index to a medium with lower refractive index, the critical angle is the angle above which there is no refracted light, and all the light is reflected. The value of this angle is given by

where n2 and n1 are the refractive indices of the second and first medium, respectively.
In the first part of the problem, light moves from glass to air (

) and the critical angle is

. This means that we can find the refractive index of glass by re-arranging the previous formula:

Now the glass is put into water, whose refractive index is

. If light moves from glass to water, the new critical angle will be
Average <u>speed</u> = (distance covered) / (time to cover the distance) =
(5m) / (15 sec) =
(5/15) (m/s) = <em>1/3 m/s</em> .
Average <u>velocity</u> =
(displacement) / (time spent traveling) in the direction of the displacement
Average velocity = (5m) / (15 sec) left =
(5/15) / (m/sec) left =
<em>1/3 m/s left</em>.
A number without a direction is a speed, not a velocity.
Answer:
Explanation:
Acceleration acts for 9 s and deceleration acts for 12 - 9 = 3 s.
Total distance covered = 990 m
initial velocity u = o
Distance covered while accelerating
s₁ = 1/2 a 9² where a is the acceleration
= 40.5 a
final velocity after 9 s
v = at = 9a
while decelerating
v² = u² - 5 x s₂
0 = (9a)² - 5 s₂
s₂ = 16.2 a²
Distance covered while decelerating = 16.2 a²
s₁ + s₂ = 990
40.5 a + 16.2 a² = 990
16.2 a² + 40.5 a - 990 = 0
a = 6.5