Raindrops are falling vertically at a speed of 120 km/h through air that is moving horizontally at a speed of 40 km/h(i.e. the wind is 40 km/h). How fast are the drops actually going?
1 Answer
Explanation:
We're asked to find the speed of the raindrops relative to a still observer (called an inertial frame of reference in physics).
We're given that the raindrops have a vertical speed of
The magnitude of the speed is found by the distance formula:
#v = sqrt((v_x)^2 + (v_y)^2)#
We have:

#v_x = 40# #"km/h"# 
#v_y = 120# #"km/h"#
The speed of the raindrops is thus
#v = sqrt((40color(white)(l)"km/h")^2 + (120color(white)(l)"km/h")^2) = color(blue)(ulbar(stackrel(" ")(" "126.491color(white)(l)"km/h"" "))#