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January 27, 2015

January 27, 2015

Posted by **James** on Wednesday, September 23, 2009 at 8:17pm.

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 -
**MathMate**, Wednesday, September 23, 2009 at 10:28pmIt 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 -
**Cole**, Tuesday, October 13, 2009 at 12:59amMore like Junior year of high school physics, this identical problem is in my textbook from last year.

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