Answer: relative motion between observer and the sound source.
Explanation: The Doppler effect states that when there is a relative motion between an observer and a sound source the frequency of sound perceived by the observer is different in frequency from the original from the source.
The mathematical back up for this claim is given below.
f' = (v+v') /(v-vs) × f
Where f' = observed frequency
v = speed of sound in air
v' = velocity of observer
vs = velocity of source
f = frequency of sound source.
From the formulae, it can be seen that a change in the value of the velocity of observer (v') and source (vs) produces different value of observed frequency (f').
Note, frequency of sound (f) is a constant.
Velocity = The speed and direction that an object is moving at
Answer:
The 3rd graph
Explanation:
A free body diagram is a diagram which shows all the forces acting on an object.
The problem asks us to find the free body diagram of block A, so we must find all the forces acting on block A.
We have 3 forces acting on block A in total:
- The force of gravity (its weight), which pushes the block downward (in the diagram, it is the force represented with 
- The tension in the rope 1, which pulls block A upwards: this force is represented with 
- The tension in the rope 2, due to the weight of block 2, which pulls block A downwards: this force is represented with 
Based on the direction of these 3 forces, the correct diagram is the 3rd one.
Full moon!
when Earth is exactly between the Moon and Sun, Earth's shadow falls upon the surface of the Moon, dimming it and sometimes turning the surface red over the course of a few hours.
