Usually, we do not walk or even stand on lightweight boat or raft because of the

Question

Usually, we do not walk or even stand on 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 (see figure A below) so that v-0. The dog then runs on top of the raft at vwith respect to the water (see figure B below). The dog has one third the mass of the raft. Find an expression for the velocity of the raft after the dog began running. (Use the following as necessary: Va) ^ A. B.

Explanation / Answer

Let mass of raft be m

then dog mass is m/3

So using momentum conservation

m*Vd i^ - (m/3 +m) V = 0

V= -0.75 Vd i^ (ans)

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