Consider a woman watching an airplane taking off. As the plane moves farther away, the relative motion in the reference frame of the woman can be determined by velocity vector diagrams. In another example, a boat and a ship are traveling apart from each other with an angle of 45°. When observed from the moving ship, the boat appears to move away at an angle higher than 45°. The velocity of the boat relative to water is 35 kilometers per hour and the ship's velocity is 40 kilometers per hour. What will be the velocity of the boat relative to the ship? Initially, list the known and unknown quantities. Label the vector triangle sketch. Make sure the sum of the angles of the triangle is equal to 180°. Using the law of sines and by substituting the magnitude of the sides and their opposite angles of the triangle, the velocity of the boat relative to the ship is calculated.