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Mechanics

Cool goIITian

Joined:	9 Oct 2007
Post:	73

20 Oct 2007 11:23:14 IST

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373

guys tell whether i am rite ..............Will rate u if u help :)

None

the last problem in hc verma.......a block is kept on thefloor of elevator atrest the elevator is descending with 12 m/s2 then find the displacement in 0.2secs

the ans is 20cm...........

first it is on floor so normail reaction N is up...... later after a while its decening with 12its N is down.......so the answer will be the diplacement in which it was decelearting with g from floor to celing......so g = a and time interval for which he asked is 0.2...apllying we get it 20 cm....but my question is whether this interpreation correct?????????

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'',' Off to a nu start!!

Blazing goIITian

Joined: 13 Jan 2007

Posts: 1289

20 Oct 2007 13:13:37 IST

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arrey the fundae is simple.......as accn of elevator is more then g so block will fall under gravity i.e a = g

so s = 1/2 .10. 0.2. 0.2 = 20 cm..

Gaurav |spideyunlimited| Ragtah

Moderator

Joined: 16 Dec 2006

Posts: 3373

20 Oct 2007 17:38:25 IST

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exactly ! lol
max acceleration of the block can be g and as lift is falling with acceleration greater than g so it is a case of free fall..
now just use g as the acceleration in the eqn of s = 1/2 at^2

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