I have a super simple question on average velocity that either I am not setting up correctly, or is itself graded incorrectly in a huge online system used by thousands of students for a very long time.
I seriously doubt the later could go uncaught.
Here's the question:
A car travels along a straight line at a constant speed of 40.0 mi/h for a distance d and then another distance d in the same direction at another constant speed. The average velocity for the entire trip is 31.5 mi/h.
What is the constant speed with which the car moved during the second distance d?
And here's my work:
V0 = 40.0 mph
Δx0 = d
V1 = ?
Δx1 = d
Vavg = 31.5 mph = ( 40.0 mph + V1 ) / 2
63 mph = 40.0 mph + V1
63 mph - 40.0 mph = V1
23 mph = V1
I've done this calculation a few times, used multiple sources to verify Vavg = ( Vf - Vi ) / 2 for constant acceleration, and even tried a few variations of the problem using different values from my book.
Stil no dice; the computer always marks my answers as "off by less than 10%".
What am I doing wrong?