Race car drivers must slow down as they make turns on the track. this is best explained by the law of inertia. which statement best describes inertia for the car going around a turn?

Car racers must slow down while taking turns at the track; because the "body in motion tends to continue at straight line and requires a force to turn."

Explanation:

As we know about the Law of Inertia that a body at rest tends to remain at rest and a body in motion tends to remain in motion with a constant velocity until an outer force is applied on it.

When we observe a car racer taking turns on the racing track, he slows down the car. This is because while moving through the corners or turns of the track, the car resists to move in straight direction due to the law of inertia whereas, the driver tends to move in another direction.

In such a situation, the car may get imbalanced and lose the grip of motion in the required direction. Hence, car racer slows the pace to make the balance and turn accordingly without any flaw.

the velocity you are looking for is made up of two parts: horizontally velocity, vh, and its vertical velocity, vv. the actual velocity of the ball will be these two parts added together, and because velocity is a vector then they will need to be added vectorially.  

neglecting air resistance etc etc.,  

the horizontal velocity component will be constant (because there is no accelerating force in the horizontal direction.  

vh = 8 ms-1  

the vertical velocity component has an accelerating force: 'g'.  

using v = u +at where a = g = 9.81 ms-2.  

the vertical component of velocity, vv = 0 + gt = vv =9.81 x 2  

vv = 19.62 ms-1 . the zero appears because the virtical component of velocity at time t=0 is zero. remember, the ball was thrown horizontally.  

how fast it will be moving (it actual path (being a parabola )) will be the vector sum of these two.  

adding vectorally gives: -  

v = sqr root (8^2 + 19.62^2) = sqr root(64+384.9) = 21.18 or 21.2 ms-1

see earlier answer