$(a)$ $(i)$ Define momentum. State its $SI$ unit.
$(ii)$ An object of mass $50 \ kg$ is accelerated uniformly from a velocity of $4 \ m/s$ to $8 \ m/s$ in $8 \ s$. Find the magnitude of the force exerted on the object.
$(b)$ State Newton's first law of motion.

(N/A) $(i)$ Momentum is defined as the product of the mass and velocity of a body. Its $SI$ unit is $kg \ m/s$.
$(ii)$ Given: Mass $(m) = 50 \ kg$,Initial velocity $(u) = 4 \ m/s$,Final velocity $(v) = 8 \ m/s$,Time $(t) = 8 \ s$.
Using the first equation of motion,$v = u + at$,we find acceleration $(a)$:
$a = (v - u) / t = (8 - 4) / 8 = 4 / 8 = 0.5 \ m/s^2$.
Using Newton's second law of motion,$F = ma$:
$F = 50 \ kg \times 0.5 \ m/s^2 = 25 \ N$.
$(b)$ Newton's first law of motion states that an object remains in a state of rest or of uniform motion in a straight line unless compelled to change that state by an applied external force.