試題詳解

5. A sled loaded with sand, slides along a horizontal frictionless track. As the sled moves, sand trickles out at a constant mass-reduced rate through a hole in the back. The speed of the sled will:
(A) decrease at a constant rate
(B) increase at a constant rate
(C) remain the same
(D) decrease at a variable rate
(E) increase at a variable rate.