Which of the following statements best describes the second law of thermodynamics?
A. Heat flows spontaneously from hot to cold, and entropy
decreases.
B. Heat flows spontaneously from hot to cold, and entropy increases.
C. Heat flows spontaneously from cold to hot, and entropy increases.
D. Heat flows spontaneously from cold to hot, and entropy
decreases.

Heat flows spontaneously from hot to cold, and entropy increases.

The second law of thermodynamics relates to the entropy of a system. According to the second law of thermodynamics, the total entropy of a system may increase or remain constant in a spontaneous process.

The implication of this is that the entropy of a system never decreases. The entropy of a system increases when heat flows from a hot to a cold body and not vice versa.

Hence, the statement that; "Heat flows spontaneously from hot to cold, and entropy increases" describes the second law of thermodynamics.

B

Explanation:

Heat flows from hot to cold to lower the temperature of hot areas and increase temperature of cold areas. The end result is that the 2 areas have the same temperature, thus increasing entropy.

one person pulls 90n one way and the other has 100n pulling the other way.

so the net force = 90 - 100 = -10n,

or the ans can be 10n if the picture shows -90n and 100n instead.

conservation of mass

mass before something happens = mass afterwards