Chapter 10, Problem 38PQ

Usually, we do not walk or even stand on a lightweight boat or raft because of the danger of falling into the water. If you have ever stepped off a small boat onto a dock, however, you have probably noticed that the boat moves away from the dock as you step toward the dock or out of the boat. A heavy dog running on a long lightweight raft presents a similar situation. At first, the raft and the dog are at rest with respect to the water (Fig. P10.38A) so that ${\stackrel{\to }{v}}_i=0$. The dog then runs on top of the raft at ${\stackrel{\to }{v}}_d=v_dî$ with respect to the water (Fig. P10.38B). The dog has twice the mass of the raft. Find an expression for the velocity of the raft after the dog began running.

FIGURE P10.38