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

ID: 1785947 • Letter: U

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

vD = vd i this is with respect to water Or wrt ground.

Applying momentum conservation for dog-plank system,


0 = (M/3)(vd) + M v

v = - vd / 3 ......Ans