Meters for mass kilograms for volume cubic meters for density kilograms per cubic meter
Answer:
The rate of change of the shadow length of a person is 2.692 ft/s
Solution:
As per the question:
Height of a person, H = 20 ft
Height of a person, h = 7 ft
Rate = 5 ft/s
Now,
From Fig.1:
b = person's distance from the lamp post
a = shadow length
Also, from the similarity of the triangles, we can write:

Differentiating the above eqn w.r.t t:
Now, we know that:
Rate = 
Thus
Scientific knowledge itself cannot have a positive or negative impact on society per se. What can have a negative or positive impact is how this knowledge is being used.
While we all enjoy a beter life due to advancements in medicine and technology for example, this was because people decided they would put certain scientific discoveries into practice and spread them among the people.
The same thing can also be said for negative scientific discoveries. While energy produced in atomic power plants per se isn't harmful, when making an atomic bomb out of it, it can be disastrous. It was the intention of doing something evil with it that might have had a negative impact on society, not the knowledge itself.