Final answer:
Mr. Smith's average velocity for the northward trip from Houston to Dallas is 56 miles per hour northward.
Step-by-step explanation:
Mr. Smith's velocity while traveling northward from Houston, TX to Dallas, TX can be calculated using the formula for average velocity: velocity (V) = distance (d) / time (T). Given that the distance (d) is 224 miles and the time (T) is 4 hours, we can calculate Mr. Smith's velocity as follows:
V = d / T = 224 miles / 4 hours = 56 miles per hour northward.
Therefore, Mr. Smith's average velocity over the course of his trip is 56 miles per hour in a northward direction.