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Sunday, September 9, 2012

Q.427. Vertical motion under gravity.

Question 427.
A Rubber ball is dropped from a height of 27m.; Each time that it hits the ground it bounces to a height 2/3 of that from which it fell. Find the total distance travelled by the ball until it comes to rest?

Answer 427.
Total distance = 27 + (2/3) * 27 + (2/3) * 27 + (2/3)^2 * 27 + (2/3)^2 * 27 + ...
= 27 [1 + 2*(2/3) + 2 * (2/3)^2 + ...]
= 27 [1 + 2*(2/3) {1 + (2/3) + (2/3)^2 + ...}]
= 27 [1 + 2*(2/3) * 1/(1 - 2/3)]
= 27 [1 + 4/3 * (3/1)]
= 135 m.

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