Answer:
about 0.04878 hours ≈ 2 minutes 56 seconds
Explanation:
You want the time until a whale-watching boat and a whale meet if the boat is traveling south at 83 km/h and the whale is traveling north at 40 km/h when they start 6 km apart.
Closing speed
The speed at which the gap between the boat and the whale is closed is the sum of their respective speeds:
closing speed = 83 km/h + 40 km/h = 123 km/h
Time
The time it takes to close the 6 km gap is ...
time = distance/speed
time = (6 km)/(123 km/h) ≈ 0.04878 h
Converted to minutes and seconds, that is about ...
0.04878 h ≈ 2 minutes 55.6 seconds
It will be about 2 minutes 56 seconds before the boat and whale meet.
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Additional comment
NOAA recommends a distance of at least 100 yards be maintained between a boat and a whale. In some areas, the recommended distance is 400 yards when approaching head-on. The recommended boat speed is 15 knots or less, about 28 km/h.