試題詳解

4. Water is flowing at 4.0 m/s in a circular pipe. If the diameter of the pipe decreases to 1/3 its former value, what is the velocity of the water downstream?
(A) 1.0 m/s,
(B) 2.0 m/s,
(C) 8.0 m/s,
(D) 16 m/s,
(E) 36.0 m/s.