Scientists can tell this by looking at seismic waves released by earthquakes. ( if you need me to elaborate more ask)
1. D
2. A
I’m not sure on 3
Objects repel and attract because of a thing called electrostatic attraction. When objects have the same charge (positive or negative), then they will repel, and if they have opposite charges then they will attract
Answer:
A. 
B. t = 50 s
Explanation:
A. The vectorial equation of the person who is getting closer to the other person is:

r: position vector
v: speed vector = 6m/s i (if you consider the motion as a horizontal motion)
Then, you replace and obtain:

B. The time is:

d: distance to the observer = 300m
v: speed of the person on the car = 6.00 m/s
