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Mechanics

Blazing goIITian

Joined:	23 Jan 2008
Post:	334

27 Jan 2009 19:09:35 IST

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441

laws of motion

None

if u jump barefooted on a hard surface,ur legs get injured.but they r not injured if u jump on a soft surface .why?

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Comments (7)

A$PIRing HiGh - dEv aDitYa

Blazing goIITian

Joined: 13 Mar 2008

Posts: 540

27 Jan 2009 19:29:06 IST

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Acc. to me the hard surface is rigid enough and following Newton,s 3rd Law, it complety apply's force(our weight) on our foot and since time of impact is minute, our legs get injured, but on a soft surface, Newton,s 3rd law does not apply completely. It retains much fraction of the force(our weight) and thus we are not injured.Please rate if satisfied.

PATHFINDER

Blazing goIITian

Joined: 13 Dec 2008

Posts: 456

27 Jan 2009 19:32:17 IST

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no i think legs r hurt because potential energy is completely converted into tension......

rafa in revival mode

Blazing goIITian

Joined: 25 Jan 2009

Posts: 311

27 Jan 2009 19:53:45 IST

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you all are wrong how can potential energy convert into tension.tension is a force not energy.and newton was not mad.his laws are valid in all situations.the given fact is due to that impulse is given by average force into time.time of impact in case of hard surface is very less so velocty gets zero in less time so average force becomes very large. .in case of a soft surface averageforce transferred is very less because of more time of contact .

10904him

Hot goIITian

Joined: 29 Dec 2006

Posts: 191

27 Jan 2009 20:05:00 IST

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Just compare rate of change of momentum...i.e forcelessetr on soft surf due to compression of surface...

Murali G

Forum Expert

Joined: 15 Jul 2007

Posts: 395

27 Jan 2009 20:12:57 IST

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Friends,

This is the qn connected with impulse. Impulse = f x t If t is increased, the effect of force decreases. When he jumps with shoes on, the cushion present on the sole of the shoes will increase the time interval during which impulse is acting, as a result effect of force on the foot decreases. On the other hand, if he jumps with bare foot t is small and large force acts on the feet and the person gets hurt. Because of the same reason, a cricket fielder pulls his hands while catching a ball. Cheers

Himanshu Gupta

New kid on the Block

Joined: 26 Dec 2008

Posts: 12

27 Jan 2009 20:17:45 IST

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in hard surfaces change in momentum occurs in relatively less time as compared to soft surface thus we expierence greater impulsive force

plz rply

sneha

Blazing goIITian

Joined: 17 Mar 2008

Posts: 1243

27 Jan 2009 21:36:51 IST

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rafa,rao sir and himanshu are right.

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