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anchitsaini (4357)

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So , the conclusion i come to is that ,the answer is no (provided the height is till which the helicopter is taken to is neglegible compared to radius , which even though not given in the question seems a reasonable assumption )


 


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ultimator (401)

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Dei gokul (computer 001 ), what about angular momentum conservation da ? This is an expln to ur answer.
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computer001 (1847)

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eh??how is angular momentum conservation an explanation to my logic???


my explanation is basic kinematics..


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computer001 (1847)

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@ feynmann:


im not talkin abt any external force @ all!!


if the man jumps on a bus he comesback to the same position if bus moves st..


but wat abt in a merry go round?? it has circular motion...a man jumping WILL NOT land on the same spot cuz he is give a tgt velocity but the belt does not (in the material sense)move in the tgt direction!! so in circular motion this jumping will not land the man on same position


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feynmann (2236)

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Remember H<<R


so it is basically a one dimensional plane kinematics , not a circular one !!


But if u want to be veryyyyyyyyyyyyyyyy precise , then it has to be given a very careful thought . U have to solve the differential eqn of motion .


And then we can come to the exact solution .


Do u wanna try ?

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computer001 (1847)

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ofcourse im talkin abt jumping to a high enuf height...otherwise wats the pt of discussing this topic???


if it was some negligible height, then anchit cud have jus jumped and got his answer!!


n im only interested in the logic and reasoning not interested in solving..


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computer001 (1847)

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and im not trying to be "veryyyyyyyyyyyyyyyy precise".. im jus talkin of the fundas..and i fail to understand y an expert is trying to challenge me to solve some complex diff eqn.. if v students cud do all tht then wat r u experts there for???


no offence to any expert..


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little_genius (295)

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the answer shud b no . .. i .e he will not reach the same pt..
bcoz when the superman was on earth its W(ang . vel) was equal to that of earth..
now when he lifts up the tangntl vel. remains same as that on the ground b4 , but since the ang. vel decreases bcoz the radius frm the centre to the man bcoms > than radius of earth ...

so as long as he remains at some height abv the grnound ,his angular vel.W remains smaller than that of the earth..
so the place benteath him constantly keeps changing and he DOES NOT REACH THE SAME PLACE AS B4...

except in one case when the time of arrivaal is such that earth has completed one full roration.. and the place benath him after changing constantly has come to the same place due to the full rotation of the earth.....

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feynmann (2236)

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@ computer .


Let's be serious !!


First of all , the analogy by which u are drawing conclusion is ENTIRELY FALSE . That's because in the merry - go-round u don't have any appreciable gravitational force towards it . But in the problem u HAVE TO CONSIDER the gravitational force on the helicopter or whatever .


So now explain ur reasoning .


I think  now it would be clear to u why I was telling to solve the differential eqn of motion . Got it ?


Now the problem can be formulated as follows:


Consider a ball given an upwards velocity v wrt earth which is rotating at a constant angular speed w. Find the time when the ball hits the Earth again .Also find the angular displacement of the ball on hitting the earth .


If earth moves by same amount by the same time then it will land at the same point , otherwise not .


Do u agree with this formulation ? If agree then plz go ahead using spherical polar co-ordinates . That's not  so difficult but may be time-consuming ,


Anyway , I am pleased with ur clear-cut comment . An academic comment , I believe( Unlike some experts ),should be made like this .

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d_utkarsh (10)

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due to inertia, we also rotate along with the earth


so.... u wont reach america

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feynmann (2236)

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Anyway ,after some calculation in polar co-ordinates I have obtained the final differential eqn in the formulated problem as follows:


 


\frac{d^2r}{dt^2}= \frac{R^4w^2}{r^3}-\frac{GM}{r^2}


The initial conditions are at t=0, r=R and \frac{dr}{dt}=v


where R is the radius of the earth , M = mass of the earth and v is the velocity at which it was initially thrown up into the air ,wrt earth .


Now we have to solve this eqn to find the non-zero time when r=R .


And then proceed in the way in my previous post .


 

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feynmann (2236)

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See, the differential eqn is not difficult itself but the calculations are a bit lengthy .


To solve it , u may put p = dr/dt


so LHS = pdp/dr


Now integrate both sides wrt r .


Then find p ( = dr/dt).


Then solve r(t) .( all the initial conditions are specified )


Please someone try it !!!

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atul_sinha89 (46)

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no it is not possible..

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atul_sinha89 (46)

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i agree with the expert...

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