B. Newton's First Law, I'm pretty sure. The first states that an object in motion stays in motion, and an object at rest stays at rest until an outside force is applied, and that seems pretty relevant.
Answer:

Explanation:
is the angle between the velocity and the magnetic field. So, the magnetic force on the proton is:

A charged particle describes a semicircle in a uniform magnetic field. Therefore, applying Newton's second law to uniform circular motion:

is the centripetal force and is defined as:

Here
is the proton's speed and
is the radius of the circular motion. Replacing this in (1) and solving for r:

Recall that 1 J is equal to
, so:

We can calculate
from the kinetic energy of the proton:

Finally, we calculate the radius of the proton path:

Gain in decibels is given by;
Gain db = 10*log (Po/Pi), where Po = Power output, Pin = Power input
Substituting;
Gain in db = 10 * log (50/5) = 10 db
Answer:
If the force remains the same, the acceleration would decrease
Explanation:
According to Newton's second law, the acceleration of an object is given by

where
F is the force applied to the object
m is the mass of the object
As we see from the formula, the acceleration a is inversely proportional to the mass, m. Therefore, if the force F remains constant, this means that if the mass of the skateboarder increases, then the acceleration will decrease.