A lumberjack (mass=98 kg) is standing at rest on one end of a floating that is a

Question

A lumberjack (mass=98 kg) is standing at rest on one end of a floating that is also at rest. The lumberjack runs to the other end of the log (mass=230 kg), attaining a velocity of +3.6 m/s relative to the shore, and then hops onto an identical floating log that is initially at rest. Neglect any friction and resistance between the logs and the water. (a) What is the velocity of the first log just before the lumberjack jumps off? (b) Determine the velocity of the second log if the lumberjack comes to rest on it.

Explanation / Answer

(a) As there are no external forces acting on the system the net acceleration of the centre of mass must be 0. Hence the log moves with a velocity = 98 X 3.5 / 275 = 1.247m/s The direction is opposite to that of the man hence velocity = - 1.247m/s (b) Initial momentum =Final momentum 98 X 3.5 = (98 + 275) X v This gives v = 0.920m/s

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