The answer that best fits the blank provided above is MECHANICAL ADVANTAGE. Given that in simple machines, output should not be greater than the input therefore, the Mechanical advantage of a simple machine has its input forces multiplied instead which results in force amplification. The answer for this would be option A.
Answer:
Acceleration =0
Explanation:
There are two forces on the box in horizontal direction.
First one is horizontal component of 30N at 45°.

Another one is given in opposite to direction of motion mean opposite to this force.
Which is = 2.22 N
Now we know F (net) =mass*acceleration(center of mass)
21.2-21.2 =10*acceleration
acceleration =0
I'm not completely sure but i think it's false