Math Is Fun Forum

mathitfun224

Member

Registered: 2016-11-07

Posts: 1

Series and Sequence Urgent Problem.

A ball takes 1 second to hit the ground when dropped. It then takes 90% of this time to rebound to its new height and this continues unil the ball comes to rest.

a) Show that the total time of motion is given by 1 + 2(0.9) + 2(0.0)^2 + 2(0.9)^3 + .....
b) Find Sn for the series in a.
c) How long does it take for the ball to come to rest.

I understand the concept of how 1 + 2(0.9) + 2(0.9)^2 + 2(0.9)^3 + ...

but I dont get how to get section b, the answer should be 19 - 20 x (0.9)^n

???

evene

Member

Registered: 2015-10-18

Posts: 272

Re: Series and Sequence Urgent Problem.

This is an exponential decay...

thickhead

Member

Registered: 2016-04-16

Posts: 1,086

Re: Series and Sequence Urgent Problem.

Leave the first term. Others are in Geometric progression.Sum them up and you get the result.

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