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March 26, 2017

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Illinois Jones is being pulled from a snake pit with a rope that breaks if the tension in it exceeds 755 .

If Illinois Jones has a mass of 70.0 and the snake pit is 3.90 deep, what is the minimum time that is required to pull our intrepid explorer from the pit?

Can anyone help?
Confused

  • College Physics - ,

    It is a very nice problem, except that the question lacks units. I will assume metric units, which will make g = 9.8 m/s/s.
    I restate the problem as follows:
    "Illinois Jones is being pulled from a snake pit with a rope that breaks if the tension in it exceeds F = 755 N.

    If Illinois Jones has a mass m of 70.0 kg and the snake pit is h=3.90 m deep, what is the minimum time that is required to pull our intrepid explorer from the pit? "

    The force on the rope just to suspend Jones in the air would be mg=686N.
    Reserve capacity for acceleration (assume the rope has no mass) is therefore 755-686=69N
    Mass, m = 70 kg
    Using F=ma
    Acceleration, a = 69/70 kg = 0.986 m/s/s
    Assuming the lift starts from initial velocity v0=0 m/s,
    the time t (seconds) required to lift him through h=3.9 m is given by
    h = v0.t + (1/2)at²
    in which all variables are known except t.
    So substitute all the known values and solve the resulting equation for t (in seconds). Do not retain the negative value of t. I believe it is under 3 seconds.

  • College Physics - ,

    More like Junior year of high school physics, this identical problem is in my textbook from last year.

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