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![[Post New]](/templates/default/images/icon_minipost_new.gif) 4 Sep 2007 21:37:42 IST
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The friction coeff b/w an athlete's shoes & ground is o.90.Suppose a superman wears these shoes & races for 50m.There is no upper limit on his capacity of running at high speeds (a).Find the minimum time that he will have to take in completing the 50m starting from rest? (b).Suppose he takes exactly this minimum time to complete the 50m ,what minimum time will he take to stop? Experts plz tell the ques with complete solution means how will the friction act on him ,which friction & why that friction only acts.Wat motion he will do ti get dat friction ,how will he stop etc.. Plz help me i am in gr8 trouble
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PLZ DONT RATE ME FOR MY ANSWERS,IF U WANT TO COMPLIMENT ME THEN JUST HELP ANY OTHER IN FUTURE AS I AM DOING IT NOW
FILL THE UNFORGIVING MINUTE WITH 60 SECONDS THEN THE LIFE WILL BE YOURS
The woods are lovely, dark &deep
But I have promises to keep
And miles to go before I sleep
And miles to go before I sleep
-Robert Frost
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5 Sep 2007 02:36:28 IST
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We run because we push the ground backwards and ground pushes us forward by friction.
So maximum force that can be exerted by ground on superman = 0.9mg and he can accelerate at best by 0.9g
So to finish 50m he must take sqrt(2*50/0.9g)=10/3 sec (taking g=10m.s^2)
To stop again his deacceleration can at best be 0.9g so he must atleast take 50 m
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Krishna Gopal Singh
B.Tech Chemical Engg
IIT Delhi 2002
Currently doing PhD from IIT Delhi |
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5 Sep 2007 16:17:44 IST
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isr but which friction will act kinetic or static coz if kinetic friction acts then wat will be the case when he will take more time than this minimum time & if static friction acts then how can a person move coz it just balances the force exerted by us on earth so it will not allow us to move
plz sir make the answer more clear
plzz
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PLZ DONT RATE ME FOR MY ANSWERS,IF U WANT TO COMPLIMENT ME THEN JUST HELP ANY OTHER IN FUTURE AS I AM DOING IT NOW
FILL THE UNFORGIVING MINUTE WITH 60 SECONDS THEN THE LIFE WILL BE YOURS
The woods are lovely, dark &deep
But I have promises to keep
And miles to go before I sleep
And miles to go before I sleep
-Robert Frost
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6 Sep 2007 14:08:35 IST
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hey plz any expert give ans to my query completely
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PLZ DONT RATE ME FOR MY ANSWERS,IF U WANT TO COMPLIMENT ME THEN JUST HELP ANY OTHER IN FUTURE AS I AM DOING IT NOW
FILL THE UNFORGIVING MINUTE WITH 60 SECONDS THEN THE LIFE WILL BE YOURS
The woods are lovely, dark &deep
But I have promises to keep
And miles to go before I sleep
And miles to go before I sleep
-Robert Frost
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6 Sep 2007 14:42:54 IST
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It has to be kinetic friction .... the person is moving and not stationary (in equilibrium) .......
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This is just da beginning .....
Ankur |
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7 Sep 2007 10:39:50 IST
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but i am not understanding that in which case he will take more time to run dat distance then this minimum time
plzzzzzz anyone
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PLZ DONT RATE ME FOR MY ANSWERS,IF U WANT TO COMPLIMENT ME THEN JUST HELP ANY OTHER IN FUTURE AS I AM DOING IT NOW
FILL THE UNFORGIVING MINUTE WITH 60 SECONDS THEN THE LIFE WILL BE YOURS
The woods are lovely, dark &deep
But I have promises to keep
And miles to go before I sleep
And miles to go before I sleep
-Robert Frost
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7 Sep 2007 13:51:26 IST
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look we push the ground and ground pushes us forward following newtons third law
here friction coefficient is 0.9.
Max friction that can act = 0.9mg
This means if we apply force less than 0.9mg, then the ground will apply an equal force on us in forwards direction
But if we were to push the ground with a force grtr than 0.9mg, then the feet with which we will push will slip in backwards direction coz the ground wont be able to oppose the whole force
So we will have to consider static friction in this ques
Hope this clears ur doubt....
Rate if it does....
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10 Sep 2007 20:00:57 IST
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hey yaar but if the friction is static then it will only balance the force we exerted backward then there will be no force on us
then how will it creates acceleration on us
plz explain dat
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PLZ DONT RATE ME FOR MY ANSWERS,IF U WANT TO COMPLIMENT ME THEN JUST HELP ANY OTHER IN FUTURE AS I AM DOING IT NOW
FILL THE UNFORGIVING MINUTE WITH 60 SECONDS THEN THE LIFE WILL BE YOURS
The woods are lovely, dark &deep
But I have promises to keep
And miles to go before I sleep
And miles to go before I sleep
-Robert Frost
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13 Sep 2007 19:55:59 IST
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hey p[lz any one explain it to me
i am very confused regarding this
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PLZ DONT RATE ME FOR MY ANSWERS,IF U WANT TO COMPLIMENT ME THEN JUST HELP ANY OTHER IN FUTURE AS I AM DOING IT NOW
FILL THE UNFORGIVING MINUTE WITH 60 SECONDS THEN THE LIFE WILL BE YOURS
The woods are lovely, dark &deep
But I have promises to keep
And miles to go before I sleep
And miles to go before I sleep
-Robert Frost
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13 Sep 2007 23:25:51 IST
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dear prakhar,
consider forces acting on d body(newtons 2 law).
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its easier to crack jee than 2 crack cet. |
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