Question about falling bodies

From: Rob Bruce (robbruce_at_ozemail.com.au)
Date: 02/12/05 

Date: Sat, 12 Feb 2005 12:58:01 +1100

Hi all,

I need some help answering a pretty basic question that I just can't seem to
get right.

I have a mass of 100kg attached to a rope. The rope has been shown to break
if a force of 4200N is applied to it.

How far does the mass have to fall to exert a force of 4200N on the rope (I
don't know the length of the rope but am allowed to assume the 4200N force
will be able to build up before the rope applies a breaking force - i.e. I
can assume that the rope is just long enough for the minimum force needed to
snap it to be built up by the falling mass).

Mass starts at rest (i.e. initial velocity =0)

I am allowed to ignore all forces except gravity (i.e no angular forces mass
is assumed to fall directly to earth, no air resistance etc).

I started off thinking momentum was the key and went through the classical
formulas to back calculate the velocity and displacement but that strikes me
as too simplistic.

So I throw myself on the mercy of the group to give me some thoughts.....

thanks

Rob

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