Time / distance problem

[ss_0001]

Hi,

Two aircraft depart from London. The first takes off at 05:39, and maintains an average cruising speed of 510mph. The second aircraft departs at 06:39 and travels at 550mph. By which time will the second aircraft catch up with the first?

I calculated the head start of the first aircraft is 510 miles (1hr at 510mph).
The closing speed is 40mph, therefore time to catch up is 510/40 = 12.75, or 12hrs 45mins.
Therefore adding 12hrs 45mins to 0639, gives the catch up time of 19:24.

The answer shown was 19h (?) Maybe it was just rounding, or did I make a mistake?

thanks.

 

[Deleted member 4993]

Hi,

Two aircraft depart from London. The first takes off at 05:39, and maintains an average cruising speed of 510mph. The second aircraft departs at 06:39 and travels at 550mph. By which time will the second aircraft catch up with the first?

I calculated the head start of the first aircraft is 510 miles (1hr at 510mph).
The closing speed is 40mph, therefore time to catch up is 510/40 = 12.75, or 12hrs 45mins.
Therefore adding 12hrs 45mins to 0639, gives the catch up time of 19:24.

The answer shown was 19h (?) Maybe it was just rounding, or did I make a mistake?

thanks.

With the assumption that the planes are flying on the same route and direction - your answer is correct.

This is a sloppy problem. The planes will be flying across time zones and the time will change. Time will also change according to their flying direction. So if the planes fly out of London exactly N-S direction - then your answer will be correct. To make the Book's answer correct - those will have to fly slightly to West (and gain those 24 min).

 

[Denis]

The planes will be flying across time zones and the time will change. Time will also change according to their flying direction. So if the planes fly out of London exactly N-S direction - then your answer will be correct. To make the Book's answer correct - those will have to fly slightly to West (and gain those 24 min).

All that's correct...EXCEPT last Saturday when the end of the world took place at 6 pm:
for rapturical reasons, twas then 6 pm all over the joint...