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

Question

A lumberjack (mass = 98 kg) is standing at rest on one end of a floating log (mass = 290 kg) that is also at rest. The lumberjack runs to the other end of the log, attaining a velocity of +2.8 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? (Indicate the direction of the velocity by the sign of your answers.)


(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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