The $SI$ unit of force is

$(a)$ When a motorcar makes a sharp turn at a high speed,we tend to get thrown to one side. Why?
$(b)$ State Newton's first and third law of motion.
$(c)$ $A$ force of $5 \ N$ gives a body of mass $m$ an acceleration of $10 \ m \ s^{-2}$. Calculate the mass of the body in grams.

State whether the following statement is true or false:
$1 \ N$ is the force that produces an acceleration of $1 \ m \ s^{-2}$ in a body of mass $1 \ g$.

In the following cases,identify the direction of the net force acting on the objects:
$(a)$ $A$ car drives around a circular race track at a constant speed.
$(b)$ Earth moving around the sun.
$(c)$ $A$ ball,rolling across a grassy field,slowly comes to a stop.

State Newton's second law of motion.

Suppose a ball of mass $m$ is thrown vertically upward with an initial speed $v$. Its speed decreases continuously until it becomes zero. Thereafter,the ball begins to fall downward and attains the speed $v$ again before striking the ground. It implies that the magnitude of the initial and final momentum of the ball are the same. Yet,it is not an example of the conservation of momentum. Explain why?