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    human09fishie Posts: 5, Reputation: 1
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    #1

    Nov 9, 2008, 07:27 AM
    Collisions and Momentum
    A ball is dropped from a height of 1.60 m and rebounds to a height of 1.40 m. How many rebounds will the ball make before losing at least 90% of its energy?
    ebaines's Avatar
    ebaines Posts: 12,131, Reputation: 1307
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    Nov 11, 2008, 01:52 PM

    The energy of the ball is proportional to the height it reaches (PE = mgh). So since after one bounce the ball reaches 87.5% of its original height (1.4m/1.6), and assuming that the ball losses a fixed percentage of its remaining energy with each bounce, you can calculate how many bounces it takes to have only 10% of its original energy left by solving for n:

    (1.4/1.6)^n <= 0.1

    Do you know how to solve this for n? You can either use logarithms or just guess at values of n and plug them into your calculator until you find one that works.
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