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A quirky math problem about a rubber ball dropping from a specific height?
A rubber ball is shot vertically to a height of 20 feet and allowed to drop. Each bounce is 80% as high as the previous bounce. What is the total distance the ball travels? Use the numerical answer only. Example: 1200
Correct Answer will be chosen as best answer! PLEASE provide a brief explanation.
5 Answers
- ?Lv 45 years ago
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- 1 decade ago
Let the height to which the ball is thrown initially be x.
After one bounce the height to which it goes is (80/100)x=x*0.8
After two bounces the height to which it goes is (80/100)(x*0.8)=x*(0.8)^2
Similarly for the 'n'th bounce the ball goes to a height of x*(0.8)^n
And so on till the ball comes to rest.
Total distance travelled by the ball=x+(x*0.8)+(x*0.8^2)+......+(x*0.8^n)+.......infinity
This is a geometric series of the form
a+a*r+a*r^2+....+a*r^n+....
which has a solution a/(1-r) provided that r<1 .If r>1 the answer is infinite
Here,
a=x
and r=0.8
We have that r<1 hence we can apply the above formula,
a/(1-r)=x/(1-0.8)=5*x
Here,
x is given as 20
Hence the total distance travelled by the ball is 5*20=100 feet.(answer)
The
- Anonymous1 decade ago
20 + .8(20) + .8(.8(20)) + .8(.8(.8(20)))... and so on. Multiply all by 2 to incorporate round trip.
20(2) + 16(2) + 12.8(2) + 10.24(2) + 8.19(2) + 6.55(2) + 5.24(2) + 4.19(2) + 3.35(2) + 2.68(2) + 2.14(2) + 1.71(2) + 1.37(2) + 1.1(2) + .88(2) + .7(2) + .56(2) + .45(2) + .36(2) + .29(2) + .23(2) + .18(2) + .14(2) + .11(2) + .09(2) + .07(2) + .06(2) + .05(2) + .04(2) + .03(2) + .02(2) + .01(2)
199.66 feet
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- Anonymous1 decade ago
20+(.8*20)+(0.8*(0.8*20))+.......and it keeps going until the hight of the ball reaches closer to 0....you add all of them up and get an ansswer..