(c) If a Boston police officer happens to get you and the Porsche on the radar gun at the instant the Porsche passes you, will either of you be pulled over for speeding? Assume the speed limit is 50 km/hr.

You're traveling at a constant speed of 40 km/hr, which is under the speed limit.

To figure out how fast the Porsche is going at t = 5.631 seconds, use:

v = v_o + a t = 0 + (3) (5.631) = 16.893 m/s.

Converting this to km/hr gives a speed of 60.8 km/hr, so the driver of the Porsche is in danger of getting a speeding ticket.