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Physics help please?

An 78-kg lumberjack stands at one end of a 390-kg floating log. Both the log and the lumberjack are at rest initially.

A)The lumberjack then trots toward the shore with a speed of 2.7 m/s relative to the shore. What is the speed of the log relative to the shore? Ignore friction between the log and the water.

B)If the mass of the log were greater, would its speed relative to the shore be greater than, less than, or the same as the speed found in part A?

C)Check your answer to part B by calculating the speed relative to the shore for a 460-kg log.

1 Answer

  • ?
    Lv 7
    1 month ago
    Favourite answer

    Let's assume that the log is perpendicular to the shore, and that the lumberjack is at the far end of it.

    A) The center of mass doesn't move (since there are no external forces applied to our l'jack/log system), so

    390kg*V - 78kg*2.7m/s = 0 → → V = 0.54 m/s

    B) The log's speed would necessarily decrease. (If it were infinitely massive, it wouldn't move!)

    C) V = 78kg*2.7m/s / 460kg = 0.46 m/s

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