19) This question asks us the distance the boat drifts downstream by the time it reaches the other side of the river. First, let's find the time it takes for the boat to get to the end of the river.
Since the boat is not accelerating we can use a simplified version of one of the kinematic equations. dX/dt is the derivative of position with respect to time; if you have not taken calculus, it will be easier to think about the problem with the last form of velocity.
Using only the x-components, we can find the time it takes for the boat to cross the river.
The boat takes 10 seconds to cross the river; this means the boat moves down the river in the -y-direction for 10 seconds at 2 meters per second.
Since the boat moves -20 meters along the y-axis, the relative motion would equate to 20 meters in the -y-direction, which, in other words, means 20 meters downstream.
Answer: C
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