Final answer:
The second bus catches up with the first bus in 2 hours.
Step-by-step explanation:
To calculate how much time passes until the second bus catches up with the first bus, we need to find the distance between them when the second bus starts and the relative speed between the two buses.
When the second bus starts, the first bus has already traveled for 1 hour (from 4:00 p.m. to 5:00 p.m.) at a speed of 40 mph. Therefore, the first bus has covered a distance of 40 miles.
The relative speed between the two buses is the difference in their speeds, which is 60 mph - 40 mph = 20 mph.
Using the formula: t = d / v, where t is the time, d is the distance, and v is the speed, we can calculate the time it takes for the second bus to catch up with the first bus:
t = 40 miles / 20 mph = 2 hours.
Therefore, it takes 2 hours for the second bus to catch up with the first bus.