Question
In the Appalachians, along the interstate, there are ramps of loose gravel for semis that have had their brakes fail to drive into to stop. Design an experiment to measure how effective this would be.
Final Answer
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Solution video
OpenStax College Physics for AP® Courses, Chapter 7, Problem 32 (Test Prep for AP® Courses)
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Video Transcript
This is College Physics Answers with Shaun Dychko. These escape ramps are common also in British Columbia (where I live) and you have roads that go down steep mountain sides and there's a ramp off the side of the road covered in gravel and the ramp goes back up a hill to some extent and it's using both gravity and friction to stop the semi-truck that has no brakes anymore. So let's ignore the contribution of gravity to the two scenarios that we're gonna test here because the scenarios will be the same in terms of having the escape ramp equal steepness and the only difference being the amount of friction on each one having gravel and one with no gravel and you could send some... sort of... cart down this ramp and see how high it goes some height change h and that's h with gravel and here's h with no gravel and see how these heights compare and that could be your experiment and what you are expecting is that the distance traveled along the ramp is going to equal the change in kinetic energy and so you could find out how much kinetic energy it will have at the beginning of the ramp and that will be equal to the amount of potential energy it has at the top of this hill and that's divided by friction because this change in kinetic energy will equal the work done by friction and the stopping distance is inversely proportional to the friction force and there's gonna be friction in both cases; there's friction in the axles in the truck... you know... mechanism and a little bit of friction between the wheels and a smooth ramp but there's gonna be much more friction in this case with gravel and so what we expect is that friction force will be higher in the gravel scenario and therefore a correspondingly smaller stopping distance given that it will have the same kinetic energy at this bottom point in both scenarios.