[填空题]
Raindrops make an anebea hj2anqn.4+(0f l g 23can u;-ulpfq thl;,le $\theta=30^{\circ}$ with the vertical when viewed through a moving train window (Fig. below). If the speed of the train is $20 \; m/s$ (a) what is the speed of the raindrops in the reference frame of the Earth in which they are assumed to fall vertically? $m/s$
(b) what is the speed of the raindrops relative to the train? $m/s$
