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Vandaag is het 27 May 2017

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Rolling from a slope - science puzzle

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At the same time a block of iron and an equally heavy iron sphere are released from the top of a slope. Assume that the friction between the slope has a negligible effect on the velocity of the block and the sphere. Which of the two will be down first?

Explanation

Both objects are moving downwards, but the sphere will also start to rotate (which costs additional energy). The acceleration of the sphere is therefore somewhat less than that of the block. So the block will be down first. (If the sphere is solid the difference is about 20% in time).

(The kinetic energy of the block is 0.5 * m * v^2, and that of a solid sphere: 0.7 * m * v^2).