If the angle is either 0 or 180, that means that there is either negative or positive work, so A and D are not correct.
If the angle is 45, then there is still some work involved.
The only option where there is no work done by a force is B. when the angle is between the force and displacement is 90.
Answer: A. Red light is reflected
Explanation:
Answer:
f'=5.58kHz
Explanation:
This is an example of the Doppler effect, the formula is:
Where f is the actual frequency, 
is the observed frequency, 
is the velocity of the sound waves, 
the velocity of the observer (which is negative if the observer is moving away from the source) and 
the velocity of the source (which is negative if is moving towards the observer). For this problem:
Mental and non mental, an ionic bond is a type of chemical bond formed through an electrostatic attraction between two oppositely charged ions. Ionic bonds are formed between a cation, which is usually a metal, and an anion, which is usually a nonmetal.
