Final answer:
The speed of the raindrops measured by an observer in a moving car, with rain falling at 4 m/s and the car moving at 18.5 m/s, is approximately C. 18.9 m/s, found by vector addition and Pythagoras' theorem.
Step-by-step explanation:
To calculate the speed of the raindrops as measured by an observer in a moving car, we need to consider the concept of relative velocity in Physics. Given that raindrops fall vertically at 4 m/s and the car is moving horizontally at 18.5 m/s, we use vector addition to find the resultant velocity of the raindrops relative to the observer in the car.
The vertical and horizontal motions are independent of each other and can be combined using Pythagoras' theorem. The resultant speed v of the raindrops with respect to the observer in the car is given by:
v = √(v_rain^2 + v_car^2)
Substituting the given values:
v = √((4 m/s)^2 + (18.5 m/s)^2)
v = √(16 + 342.25)
v = √358.25
v ≈ 18.9 m/s
The observer in the car would measure the speed of the raindrops as approximately 18.9 m/s, which is not one of the options provided in the question. Therefore, there might be a discrepancy or typo in the options given. The correct approach has been used, but the options might need revision.