1lets take an example............let the speed be 100
so after 1st plank ........it is 100 - 5% of 100
after 2nd plank it is remaining -5% of remaining................then go on.....till u get almost zero.....................
hehe
A bullet loses 1/20 of its velocity in passing through a plank . what is the least number of planks which are required to stop the bullet.
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13 Answers
62This you have to do by finding the resistance.
v2=u2+2as
{(19/20)2-1}/2 u2 = as
For v=0,
0=u2+2a"S"
u2{(19/20)2-1}/2 = -{(19/20)2-1}/2 x 2aS
as={1 - (19/20)2} a S
So we know S in tems of s..
The ratio will givethe number of planks required.
Correction: Rectified the -ve sign :)
162no that is not how it is to be done akand.
That way the answer will be infinite :)
1hehe..i kno bhaiyya..............thts y i said till u get almost zero.........hehehe......but thts wat i do when i dont kno d perfect method...........by d way thnx for d method...............
11exactly what i dint want from you bhaiyya!
i thought you would say infinite!
that would be the more perfect and physical answer
after the nth plank velocity would be (19/20)nv
and not zero so it should be infinite
62subash...
If the planks are identical then my answer will be correct
If the planks are not identical and the question is that that every single plank will behave similary that is to reduce the velocity to 19/20th then infinity will be the answer.
62obviously this is controversial because the question of this type is more like trying to trick the student by language :)
Which IITs will not do.. and I guess i have said this many times.
The IIT JEE paper will test your concept and not your understanding of english ;)
11yeah i was giving it for all identical planks
and i realise that it is not quite relevant to JEE
1dude think logically........it has to stop sumwher.........u r gettin infinty because u r taking 5% of each upto a minute decimal place like 0.0005 which will never end but a bullet of speed 0.0005 is same as a bullet of zero velocity