From inside your apartment, you watch rain fall straight down at a constant speed of 9 m/s. Your friend L calls you as she is driving toawards the west at a constant of 90 km/hr. What with what velocity does L see the rain fall as she looks out her driver's side window?

Question

From inside your apartment, you watch rain fall straight down at a constant speed of 9 m/s.  Your friend L calls you as she is driving toawards the west at a constant of 90 km/hr.  What with what velocity does L see the rain fall as she looks out her driver's side window?

I know I'm trying to find the velocity relative to L driving.  I just don't know where to start.  How would the velocity of the rain change?

Quidditch · Answer

Be sure to take care of units conversions. From L's point of reference, the rain has the x component from her driving plus the y component of the rain falling. Find the resultant vector.

drwls · Answer

The velocity of the rain with respect to someone in the car is the vector sum of the downward rain velocity (9 m/s) and the car's speed, 90000m/3600 s = 25 m/s. Use the Pythagorean theorem for the resultant