Final answer:
The motorcycle with an acceleration of 4.2 m/s² will be moving at 12.6 m/s after 3 seconds.
Step-by-step explanation:
If a motorcycle accelerates uniformly at 4.2 m/s², we can use the basic kinematic equation for acceleration to find out how fast it is moving after a certain time. The formula looks like this: v = u + at, where v is the final velocity, u is the initial velocity (which we'll assume is 0 since it's not provided), a is the acceleration, and t is the time. In this case, after 3 seconds, the velocity of the motorcycle would be:
v = u + at = 0 + (4.2 m/s²) * (3 s) = 12.6 m/s
So, the motorcycle would be traveling at 12.6 m/s after 3 seconds, which corresponds to option A) 12.6 m/s.