I should have made this clear, we do know that the rope will act like a spring (and the force is linear). I was using F=k*Rs/R (basically the spring equation, except that the force depends on the relative stretch of the rope--how much it stretches divided by how long it is; I've checked on...
Homework Statement
A mass m is attached by a rope to car. The car accelerates to speed V before the rope becomes taut. The rope is length R and will stretch and additional length Rs. Find the maximum force on the rope. Ignore friction and assume that the rope runs parallel to the ground...