It's been a while since I've studied this, but my answers would be:
13. 5730 years. The half-life of a substance is the amount of time it takes for half of it to decay, and, according to the graph, half of the substance remained at 5730 years.
14. 10740 years. According to the graph, only 25% of the carbon remained after 10740 years.
15. 15 atoms. According to the graph, only 12.5% of the carbon remained after 16110 years. 12.5% of 120 atoms is 15 atoms.
16. 1600 atoms. According to the graph, if a sample of carbon is 10740 years old, only 25% of it remains. To find the original amount, multiply the current amount by (100% / 25%), which equals 4. So, 4. 400 atoms * 4 = 1600 atoms is the original amount.
Answer:
They would attract one another
Explanation:
The interaction between two like-charged objects is repulsive. ... Positively charged objects and neutral objects attract each other negatively charged objects and neutral objects attract each other.
Answer:
The values is 
Explanation:
From the question we are told that
The speed of the fire engine is 
The frequency of the tone is 
The speed of sound in air is 
The beat frequency is mathematically represented as

Where
is the frequency of sound heard by the people in the fire engine and is is mathematically evaluated as
![f_a = [\frac{v_s + v }{v_s -v} ]* f](https://tex.z-dn.net/?f=f_a%20%20%3D%20%20%5B%5Cfrac%7Bv_s%20%2B%20v%20%7D%7Bv_s%20%20-v%7D%20%5D%2A%20f)
substituting values
![f_a = [\frac{340 + 5 }{340 -5} ]* 500](https://tex.z-dn.net/?f=f_a%20%20%3D%20%20%5B%5Cfrac%7B340%20%2B%205%20%7D%7B340%20%20-5%7D%20%5D%2A%20500)

Thus

