Final answer:
The acceleration of a particle moving at constant speed in counterclockwise circular motion at t=5.00 s would still be the centripetal acceleration, which is directed towards the center of the circle. As there is no change in speed or radius, the centripetal acceleration remains constant at 4.0 m/s².
Step-by-step explanation:
Acceleration in Circular Motion
For an object moving in counterclockwise circular motion at constant speed, the acceleration at any given time is not zero because it is constantly changing direction. This acceleration is called the centripetal acceleration and is directed towards the center of the circle. If a particle is moving in uniform circular motion, its centripetal acceleration ac remains constant in magnitude but continuously changes direction to point towards the center of the motion path. Despite a constant speed, the constantly changing direction means the particle is accelerating.
Given that the particle is at t1 = 5.00 s, even though it moves at constant speed, its acceleration is not zero but instead is the centripetal acceleration necessary to keep it moving in a circle. This is given by the formula ac = v2 / r, where v is the linear (tangential) velocity and r is the radius of the circle.
Since we are told the particle is moving at a constant speed and no change in speed or radius is indicated, we assume the centripetal acceleration remains the same at t1 as at t=0, which is 4.0 m/s². This would be the acceleration of the particle at t1 = 5 seconds.