A railroad train travels forward along a straight track at 90.0 m/s for 1 000 m and then travels at 70.0 m/s for the next 1 000 m.What is the average velocity?
A)79.3 m/s
B)78.8 m/s
C)83.8 m/s
D)75.8 m/s
E)81.5 m/s

Question

A railroad train travels forward along a straight track at 90.0 m/s for 1 000 m and then travels at 70.0 m/s for the next 1 000 m.What is the average velocity?
A)79.3 m/s
B)78.8 m/s
C)83.8 m/s
D)75.8 m/s
E)​81.5 m/s

Quizplus · Accepted Answer

The average velocity is the total displacement divided by the total time. The displacement is 1,000 m forward (positive direction) and then 1,000 m forward (positive direction) for a total displacement of 2,000 m forward. The time to travel the first 1,000 m is t = d/v = 1,000 m / 90.0 m/s = 11.1 s. The time to travel the second 1,000 m is t = d/v = 1,000 m / 70.0 m/s = 14.3 s. The total time is 11.1 s + 14.3 s = 25.4 s. Therefore, the average velocity is (2,000 m) / (25.4 s) = 78.8 m/s (forward).

A Railroad Train Travels Forward Along a Straight Track at 90.0