Superhero Acceleration

$\text{Acceleration is the rate of change of velocity in a certain time}$ . If final velocity is greater than initial velocity $(v_f > v_u)$ the body is said to be $\color{#3D99F6}accelerating$ and if final velocity is less than initial velocity $(v_f < v_i)$ the body is said to be $\color{#D61F06}decelerating$ .

Superhero A :

It is given that he is flying faster and faster. So, $\color{#20A900}v_f > v_u$ . This means he is $\color{#3D99F6}\text{accelerating at a constant rate}$ .

Superhero B :

It is given that he is slowing down. So, $\color{#20A900}v_f < v_u$ . This means he is $\color{#D61F06}\text{decelerating at a constant rate}$ .

Superhero C :

It is given that he is flying at a constant rate. So, $\color{#20A900}v_f = v_u$ That means his $\color{#E81990}\text{velocity is constant}$ and hence $\color{#E81990}\text{acceleration is zero}$ .

$\color{#20A900}\text{Therefore, only A and C are accelerating.}$

Acceleration is the rate of change in velocity per unit time. Any time in which velocity changes, we say an object has accelerated. That means any time in which an object changes its speed (the magnitude of velocity) or direction, it is accelerating.

When objects are speeding up, they are changing their velocity with time. Therefore A is accelerating.

When objects are slowing down, they also experience a change in velocity and are therefore accelerating. When an object slows down, it decreases in velocity over time in the direction it is moving. Velocity is changing. Therefore, B is also accelerating.

C is not accelerating because they are not changing their velocity. They are flying at a constant speed in the same direction.