Question

A lumberjack (mass = 103 kg) is standing at rest on one end of a floating log (mass = 245 kg) that is also at rest. The lumberjack runs to the other end of the log, attaining a velocity of +2.47 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 justbefore the lumberjack jumps off? (Indicate the direction of thevelocity 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/s

Section 7.2 The Principle of Conservation ofLinear Momentum

Answer 1

Here is what I solved before, please modify the figures as per your question. Please let me know if you have further questions. Ifthis helps then kindly rate 5-stars.

A lumberjack (mass = 103 kg) is standing at rest on one end of a floating log (mass = 297 kg) that is also at rest. The lumberjack runs to the other end of the log, attaining a velocity of +4.27 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 (again relative to the shore) just before the lumberjack jumps off? (b) Determine the velocity of the second log (again relative to the shore) if the lumberjack comes to rest relative to the second log.

answer

a) using momentum conservation ,

103 x 4.27 + 297 x v = 0

v = - 1.5 m/s

velocity of first log is 1.5 m/s in opposite direction of lumberjack .

b) again using momentum conservation ,

103 x 4.27 + 297 x 0 = (103 + 297 ) v

v = 1.09 m/s