Question

When a body is accelerated:
A. its velocity always changes
B. its speed always changes
C. its direction always changes
D. its speed may or may not change
Which of the following is correct?

Answer 1

Acceleration is defined as the rate of change of velocity with respect to time is called the acceleration. So, acceleration is nothing but at which rate velocity changes of a body or a particle. Use the definition and check each option from the concept of the acceleration of a body.

Complete answer:
When a body is accelerated it can have two types of acceleration - one is uniform acceleration and other is non-uniform acceleration. We know that acceleration is defined as the rate of change of velocity with respect to time is called the acceleration. So, acceleration is nothing but at which rate velocity changes of a body or a particle. The mathematical expression of acceleration is given by,
$\vec a = \dfrac{{\vec v}}{t}$
where $\vec a$ is the acceleration of the body, $\vec v$ is the velocity of the body and $t$ is the time.

Now let’s check the option one by one:
A. If a body is accelerated it velocity must change since from definition we have come to know that it is the rate of change of velocity.
B. Speed is the rate of change of distance and when a body is accelerated its speed may or may not change it is specific to the motion.
C. Direction of acceleration may or may not change since it can be a constant vector for uniform acceleration but for non uniform acceleration its direction and magnitude both are subject to change.
D. From, option B we have already discussed that speed may or may not change.

So, we can see that option A and option D both are correct.

Note: The speed of the body may or may not change can be explained easily by the following examples-
-When a body moves in a circular path with uniform speed the direction of it always changes so velocity changes, since velocity changes acceleration of the body also changes.
-When a body is moving in a uniform direction with constant acceleration its velocity and speed both changes.