A 55 kg swimmer is standing on a stationary 170 kg floating raft. The swimmer th

Question

A 55 kg swimmer is standing on a stationary 170 kg floating raft. The swimmer then runs off theraft horizontally with a velocity of +3.9 m/s relative to theshore. Find the recoil velocity that the raft would have if therewere no friction and resistance due to the water.
1 m/s



ssm A lumberjack(mass = 98 kg) is standing at rest on one end of a floating log(mass = 235 kg) that is also at rest. Thelumberjack runs to the other end of the log, attaining a velocityof +3.1 m/srelative to the shore, and then hops onto an identical floating logthat is initially at rest. Neglect any friction and resistancebetween the logs and the water.(a) What is the velocity of thefirst log just before the lumberjack jumps off? (Indicate thedirection of the velocity by the sign of your answers.)
1 m/s

(b) Determine the velocity of the second log if the lumberjackcomes to rest on it.
2 m/

Explanation / Answer

(a)    Momentum of raft + swimmer = Momentum ofswimmer           ( m1 +m2 ) V 1= - m2 V2            (170 + 55 ) V1 = - 55 ( 3.9 )            Recoilvelocity of raft,   V1 = - 0.953 m/s   (opposite to swimmer ) (b)   Momentum of log + lumberjack =Momentum of lumberjack           ( m1 +m2 ) V 1= - m2 V2            (235 + 98 ) V1 = - 98 ( 3.1 )          Velocityof first log before lumberjack flies off, V1 = - 0.912m/s   ( opposite to lumberjack ) (c)    If the lumberjack comes torest after jumping on to other log, then the otherlog comes to rest           ( m1 +m2 ) V 1= - m2 V2            (235 + 98 ) V1 = - 98 ( 3.1 )          Velocityof first log before lumberjack flies off, V1 = - 0.912m/s   ( opposite to lumberjack ) (c)    If the lumberjack comes torest after jumping on to other log, then the otherlog comes to rest

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