please help.....

Asked by  | 6th Aug, 2009, 03:24: PM

Expert Answer:

 If v is the initial velocity, then the velocity after it comes out of first plank is 0.10v.

Initial KE = mv2/2 and Final KE = 0.01mv2/2.

The loss in KE as it passes through one plank = Initial KE - Final KE = 0.99mv2/2.

So the loss of KE if we use n plank's is, = n(0.99mv2/2).

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

Hence n(0.99mv2/2) = mv2/2,

which gives n = 1.01, hence 2 planks will be required.




Answered by  | 6th Aug, 2009, 07:06: PM
