题目内容：

A newspaper boy throw papers sideways(i.e.perpendicular to the side walk) onto porches of his customers while riding his bicycle along the sidewalk.The sidewalk is 15m in front of the porches.The boy throws the papers at a horizontal speed of 6.0m/s relative to himself,and rides the bicycle at a speed of 4.0m/s relative to the sidewalk.
a)With what horizontal speed do the papers actually travel relative to the ground?
b)How far in advance of the porch should the boy throw the paper,so that it lands on target?
c)If instead he waits until he is directly opposite a porch,at what horizontal angle with respect to the sidewalk should he throw he paper(at a speed of 6.0m/s relative to himself),to hit the porch?
请给出公示好么？

优质解答

a)v=√(4²+6²)=2√13(m/s)
b)s=15/6*4=10(m)
c)Because:sinα=4/6=2/3 it is α=arcsin(2/3)
arcsin(2/3) degrees backward