This shows four different ramps that all start and end the same height. if identical marbles were rolled down all four ramps, at the bottom of which one would the marble be moving the fastest?

The fastest moving marble would be C.
because, A and D wouldnt work because the up-slopes cause friction that prevent the marble from going over them. So B and C are left. Looking at C first, at the start of the slope its low, causing little friction, so it falls faster. But after this steep slope it rises a bit, this new slope angle looks very similar to B, so without equations or numbers we can assume they are close enough to be considered the same slope. Marble C would fall faster because it has greater velocity already from the beginning of the slope, so Marble C reaches the bottom quicker.

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