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Radius of turn = 1 mile
How long is the ship turning to turn 1/4 of a circle?
circumference = 2 pi r = 2 pi miles
so the ship travels pi/2 miles while turning.
speed = 25 mph assume constant
time = distance / rate = (pi/2)/25 = pi/50 hours
so the ship turns 90 degrees in pi/50 hours 1432 degrees/hour
times 1 hour/60 minute = 24 degrees/minute
times 1 minute/60 seconds = 0.4 degrees/second