A lumberjack (mass = 98 kg) is standing at rest on one end of a floating log (mass = 200 kg) that is also at rest. The lumberjack runs to the other end of the log, attaining a velocity of +4.0 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.

Question

(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.)
m/s

(b) Determine the velocity of the second log if the lumberjack comes to rest on it.

Answer 1

IF friction is neglected :), then the center of mass remains at the same position. This leads to
98*4+200V=0
solve for V. Negative number means in the opposite direction.
for the second log,
98*4=(200+98)V