21. light changes its direction when travelling through a new medium because denser mediums have a higher angle of refraction.
Answer:

Explanation:
Using kinematics equations:

Use
due to condition of distance traveled.
Solving second equation for time, there are two solutions. t=0 and

Use the expression in the first equation to have

Using trigonometric identities, you have the answer of the distance.
By doing the ratio for two different angles, you have the second answer. Due to sine function properties, the distances can be the same to complementary angles. Example, for 20° and 70°, the distance is the same.
Answer:
The correct answer is 24.
Explanation:
<em>The </em><em>nucleus</em><em> has most of the atomic mass in an atom. The </em><em>nucleus</em><em> is made up of protons and neutrons.</em>
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Answer:
B) grams
The SI unit for mass is grams.