please solve this.......

Asked by  | 4th Aug, 2009, 05:26: PM

Expert Answer:

Is the velocity reduced by 10% or to 10%?

Please verify the statement of the question.

I'll assume that it's reduced by 10%.

So if v is the initial velocity, then the velocity after it comes out of first plank is 0.90v, i.e. reduced by 10%.

Initial KE = mv2/2 and Final KE = 0.81mv2/2.

The loss in KE as it passes through one plank = Initial KE - Final KE = 0.19mv2/2.

So the loss of KE if we use n plank's is, = n(0.19mv2/2).

and this total loss has to be equal to initial KE, if we have to stop it.

Hence n(0.19mv2/2) = mv2/2,

which gives n = 5.26, hence 6 planks will be required.




Answered by  | 4th Aug, 2009, 07:57: PM

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