I'm not sure what trigonometric equation I should use for this problem:
At a certain instant, a ship was 5km south of a lighthouse. The ship was travelling westward and after 30 minutes it's bearing was S 53 degrees W. What was the speed of the ship per hour?
I used: cosθ = adjacent/hypotenuse
= (cos53) hypotenuse = adjacent
= hypotenuse = adjacent/cos53 = 5km/0.60 = 8.33km/0.5hr
Speed = distance/time = 8.33km/0.5 hr = 16.66km/hr
Is this correct. Any advice is appreciated.