## Explanation

### If an object moves with constant acceleration its velocity must

### Be constant also

Constant acceleration does not imply that the velocity is constant. In fact, velocity changes continuously when acceleration is constant. Hence, this option is **incorrect**.

### Change by the same amount each second

Constant acceleration means that the change in velocity over each second is constant. Mathematically, this is expressed as

$v(t) = v_0 + at$Where:

- $v(t)$ is the velocity at time $t$,
- $v_0$ is the initial velocity,
- $a$ is the constant acceleration.

Thus, the velocity of an object with constant acceleration changes by the same amount each second, making this option **correct**.

### Change by varying amounts depending on its speed

This is **incorrect** because, under constant acceleration, the change in velocity is not dependent on the object's current speed but rather on the constant rate of acceleration.

### Always decrease

Constant acceleration does not necessarily imply a decrease in velocity. Acceleration can be positive or negative:

- Positive acceleration increases the velocity.
- Negative acceleration (also known as deceleration) decreases the velocity.

Therefore, this option is **incorrect**.

### Summary

If an object moves with constant acceleration, its velocity must:

$\textbf{Change by the same amount each second}$