Help in Physics AS level MCQ question (edited vers.)

Okay so the Question is:

An object accelerates in a direction that is always perpendicular to its motion. What is the effect, if any, of the acceleration on the object’s speed and direction?

Option A: both Speed & Direction Changes

or

Option B: Speed is Constant but Direction changes

or

Option C: Speed changes but Direction is constant

or

Option D: both Speed and direction is constant

the Answer is B

but I'd like to know why is it so?
anyone can explain it to me?

If the acceleration is always perpendicular to the direction of motion what is the component of the acceleration and force in the direction of motion ( zero )
with nothing either speeding it up or slowing it down the speed must remain constant.

However as you have applied an acceleration and a force SOMETHING must alter.
The velocity alters but not the speed. And the big difference is that velocity has a direction and speed does not. So clearly if the speed doesn't alter yet the velocity does then the direction is what has altered.

Now you would have been taught all of this at the beginning of circular motion.
So time for a bit of revision.

What the question simply means is that the object is moving in a circular trajectory. It tries to accelerate straight, but its motion will be perpendicular to it. A good example to illustrate this is satellite orbiting around earth. Satellite tries to move in a straight line because of Newton's first law, but gravitational force is acting on satellite, pulling it close to earth and hence its motion is not produced in the direction of acceleration.

Therefore, the object is travelling at constant speed but its direction is changing continuously. You can also say that velocity of object is changing hence there is acceleration. (a = delta v / t )