19) suppose that a car traveling to the east (+x direction) begins to slow down as it approaches a traffic
light. which statement concerning its acceleration must be correct?
a) its acceleration is in the -x direction.
b) its acceleration is zero.
its acceleration is decreasing in magnitude as the car slows down.
d) its acceleration is in the +x direction.

C) Its acceleration is decreasing in magnitude as the car slows down.

Explanation:

According to the described situation the car's final velocity is less than its initial velocity, this means the car's velocity decreased as it slows down.

On the other hand, acceleration is defined as the variation of velocity in time:

If the car's velocity decreases, its acceleration is negative.  Hence, the acceleration is decreasing in magnitude as well.

okay i have so many questions. but the big one here is: um wt..f is this mess? ?

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.