A 80 -kg lumberjack stands at one end of a 423 -kg floating log, as shown in the

Question

A 80-kg lumberjack stands at one end of a 423-kg floating log, as shown in the figure. Both the log and the lumberjack are at rest initially.

A 80-kg lumberjack stands at one end of a 423-kg floating log, as shown in the figure. Both the log and the lumberjack are at rest initially. If the lumberjack now trots toward the other end of the log with a speed of 2.7 m/s relative to the log, what is the lumberjack's speed relative to the shore? Ignore friction between the log and the water. f the mass of the log had been greater, would the lumberjack's speed relative to the shore be greater than, less than, or the same as in part (a)?

Explanation / Answer

1. 380/83 = 4.5783:1.
2.7/4.5783 = .59 m/sec. the log moves in the opposite direction.
2.7 - .59 = 2.11 m/sec relative to the shore.
2. 460/83 = 5.542:1.
2.7/5.542 = .487 m/sec. the log moves in the opposite direction.
2.7 - .487 = 2.213 m/sec. relative to the shore.
B) Greater than. The log's mass is greater, so the reaction (Newton's 3rd.), having to be equal, the log moves more slowly in the opposite direction, so the lumberjack does a greater distance relative to the shore.

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