When the temperature of a gas decreases at constant volume, its
a. pressure increases.
b. mass increases.
c. pressure decreases.
d. particles move faster.

the answer is c. i just took the test

Explanation:

fgravity=10x10=100n case 1

fgravity=30x20=600n case 2

6 times more

the box does not move because you need to use a force greater than 300 n. you are only using 50 n. it needs to at least be 301 n for the box to move because then it is an unbalanced force and it will move the way that the greater force is pushing it. if you use only 300 n it will be a balanced force and will not move because the force you are exerting on the   box is the same as its force.

hope this !

im sorry if i went too in depth, i am going to include a link to a video on khan academy that will explain this.   hope that you like the video and that it explains more in detail to you.

that is the link.