In the AP Physics I Essentials book, I'm a little bit stuck on question 5 for Chapter 7 Test Your Understanding. The problem states "A marble is rolled separately down two different inclines of the same height as shown below. Compare the speed of the marble at the bottom of incline A to the speed of the marble at the bottom of incline B. Compare the time it takes the marble to reach the bottom of incline A to the time it takes to reach the bottom of incline B." There is also a picture with a ball on top of an incline that is straight, and another picture with a ball on top of an incline that is curved.

I can explain why incline B would result in greater speed resulting in faster time due to the cycloid path/Brachistochrone Curve since the marble is aided by gravity and the beginning is steeper so more PE to KE for incline B etc. etc., but I can't explain it mathematically (w/equations and all). I tried using Work-Energy theorem, but that didn't really work...Also, I'm confused on how we connect the concepts of angular motion to this problem.

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## veevian

In the AP Physics I Essentials book, I'm a little bit stuck on question 5 for Chapter 7 Test Your Understanding. The problem states "A marble is rolled separately down two different inclines of the same height as shown below. Compare the speed of the marble at the bottom of incline A to the speed of the marble at the bottom of incline B. Compare the time it takes the marble to reach the bottom of incline A to the time it takes to reach the bottom of incline B." There is also a picture with a ball on top of an incline that is straight, and another picture with a ball on top of an incline that is curved.

I can explain why incline B would result in greater speed resulting in faster time due to the cycloid path/Brachistochrone Curve since the marble is aided by gravity and the beginning is steeper so more PE to KE for incline B etc. etc., but I can't explain it mathematically (w/equations and all). I tried using Work-Energy theorem, but that didn't really work...Also, I'm confused on how we connect the concepts of angular motion to this problem.

I appreciate the help!

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