Acceleration involves speeding up, while acceleration involves slowing down. a. positive, negative c. positive, braking b. negative, positive d. both a and c

The questions answer is "a"

The answer is (a.) Positive acceleration involves speeding up, while negative acceleration involves slowing down.

What does this mean?

Acceleration as we know is a vector quantity that has both magnitude and direction. Acceleration is the rate of change of velocity. So in order for an object to accelerate, it should change its velocity.

Fast moving objects with constant velocity may be moving faster, but they are not accelerating. 

When an object is speeding up, that is, its velocity increases with time, then it is called positive acceleration

When an object is slowing down, that is, its velocity decreases with time, then it is called negative acceleration

Protons have a positive charge and, collectively, give an element its atomic number.

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