Two swimmers, chris and sarah, start together at the same point on the bank of a wide stream that flows with a speed v. both move at the same speed c (where c > v) relative to the water. chris swims downstream a distance l and then upstream the same distance. sarah swims so that her motion relative to the earth is perpendicular to the banks of the stream. she swims the distance l and then back the same distance, with both swimmers returning to the starting point.
in terms of l c and v find the time intervals required
a) for chris's round trip and
b) for sarah's round trip.
c) explain which swimmer returns first.

b.

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air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.