Physics Help Forum ships in the night

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 Jul 25th 2018, 10:57 AM #1 Junior Member   Join Date: Jul 2018 Posts: 16 ships in the night Hi folks, The velocity of ship A relative to ship B is 10.0 km/h in a direction North 45 East. If the velocity of B is 20 km/h in a direction N 60 W, find the actual velocity of A in magnitude and direction. The attachment shows my sketch. Vector A relative to B (OA in the sketch) is $\underline{a} - \underline{b}$ Vector A is AB Vector B is OB so A relative to B = AB + BO or AB - OB to calculate vector A I used the cosine rule magnitude of $AB^2 = \underline{a^2} = 10^2 + 20^2 -2.10.20 \cos 105$ $\underline{a}^2 = 603.53$ $\underline{a}= 24.6$ this is the wrong answer. Correct is 19.8 can't see where I am going wrong! Attached Thumbnails   Last edited by uxinox; Jul 25th 2018 at 11:01 AM.
 Jul 26th 2018, 02:49 AM #2 Junior Member   Join Date: Jul 2018 Posts: 16 It's OK guys. Just needed to sleep on it. Problem solved.

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