If the elevator was stationary, the scale would read exactly the weight of the person:

However, the elevator is moving with an acceleration a, so the scale reads a new value of the weight, which we call W'. Newton's second law becomes

where a' is actually the total acceleration of the person, so it's the sum of the acceleraion of the elevator and of the gravitational acceleration:

Taking the direction of g (downward) as the positive direction, we can find the value of a:


So, the acceleration of the elevator is

, with same sign of g, so it's directed downward as well.
Answer:
The correct answer is -
19 - C) parasitism
20- B) commensalism
Explanation:
Parasitism is a type of symbiotic relationship among two different organisms where one is benefited and the other is harmed. The harmed organism known as the host and the benefitted organism called the parasite. For instance, tapeworms are parasites in the human body.
Commensalism is also a symbiotic relationship but in this relationship, one symbiont is benefitted but another one neither benefitted nor harmed. For instance, Hermit crabs use the shells of dead snails for homes.
The relationship between the initial velocity, final velociy, distance, and deceleration can be expressed in the following equation.
2(a)(0.270 m) = 0² - (5.70 m/s)²
The value of a (which is the deceleration) is 0.06 m/s². Thus, the answer is that the deceleration value is approximately 0.06 m/s².
Just because there is more mass in a certain substance doesn’t mean it’s density will change. In this case, water, will not change density simply because there is more of it. I.e the ocean. The bottom of the ocean may have more pressure to it because of the weight of the water above it but if you were to take a cup of it and take it to the surface it wouldn’t sink.