(II) A motorboat whose speed in still water is 4.30 m/s must aim upstream at an angle of 23.5° (with respect to a line perpendicular to the shore) in order to travel directly across the stream. 
(b) What is the resultant speed of the boat with respect to the shore? (See Fig. 3–33.)

(II) Two cars approach a street corner at right angles to each other (Fig. 3–57). Car 1 travels at a speed relative to Earth v₁ₑ = 35 km/h, and car 2 at v₂ₑ = 55 km/h . What is the relative velocity of car 1 as seen by car 2? What is the velocity of car 2 relative to car 1?

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(II) Raindrops make an angle θ with the vertical when viewed through a moving train window (Fig. 3–55). If the speed of the train is vₜ , what is the speed of the raindrops in the reference frame of the Earth in which they are assumed to fall vertically?

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(II) (a) At what upstream angle must the swimmer in Problem 71 aim, if she is to arrive at a point directly across the stream? (b) How long will it take her?

(II) An airplane is heading due south at a speed of 688 km/h. If a wind begins blowing from the southwest at a speed of 85.0 km/h (average), calculate 

(a) the velocity (magnitude and direction) of the plane, relative to the ground, and . [Hint: First draw a diagram.]

A boat on a river is traveling from a pier to a point 500 m upstream (against the river's current). The current flows at 4 m/s. If the boat makes the trip in 250 s, what is the speed of the boat relative to the water?