Berkeley Review Physics I Figure 1-12

[xwang]

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It has been a while since I had physics and I did not do well in mechanics, can someone please explain BR Physics I Figure 1-12? Which equation was used to get the four distances the ball traveled? What does the 20 in the equation refer to?

Help!

Thanks

 

[Chrisz]

You know rolling down a hill is just linear acceleration at a constant rate. D=distance traveled. D=0.5g(sin(theta))t^2. The problem did not give us theta. What to do? So weired Huh? Just kidding. Since they measured how far it has traveled at a certain time intervals, we can simply make D=kt^2 since the term is just a constant.
For time=1, 20cm k(1)^2=20 k=20 , so the equation becomes D=20t^2