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Mechanics
21 Sep 2007 17:59:41 IST
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James Bond
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21 Sep 2007 18:12:13 IST
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coz this isnt free fall, ie the object isnt being dropped it's pushed.
so gravity cancels the effect of push upto an extent during the downward motion...and hence the time elapse
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21 Sep 2007 23:56:31 IST
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Okay.....
The hall is gravity free. No air. So no resistance.
I think when the man pushes the pillow he will himself be pushed in opposite direction with the speed of 0.8 ft/s (Apply Law of conservation of linear momentum).
Actually time of decent = time of ascent but during ascent the pillow has to travel a greater distance as the man himself is rising. So considering relative velocities, the velocity of pillow decreases
:-):-)
The hall is gravity free. No air. So no resistance.
I think when the man pushes the pillow he will himself be pushed in opposite direction with the speed of 0.8 ft/s (Apply Law of conservation of linear momentum).
Actually time of decent = time of ascent but during ascent the pillow has to travel a greater distance as the man himself is rising. So considering relative velocities, the velocity of pillow decreases
:-):-)
22 Sep 2007 11:00:48 IST
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well a man who is pushing the pillow with8ft/sec ..is also thrown up with the same speed in opp dir...so if total distane =16ft...and total yime is 2 sec..(descent+ascent).will it not the same for the man?so why is not time of decent=ascent ????
22 Sep 2007 11:42:04 IST
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Hello Ayesha ,
The Answer to this is simple.
Although there is no Gravitation in the room but both the
bodies will continue to follow "Conservation of momentum"
In your Question applying ,
m1v1=m2v2
Here putting the values you will get :
50*v1 = 5*8
v1 = 0.8 ft/s
Now from here we get that when the pillow is travelling
at 8 ft/s the man is moving at 0.8 ft/s upwards and as
there is no Resistance will continue to move in 0.8 ft/s.
The time of ascend = time of descend but as the pillow
reaches the man's head so it has also got to travel the
distance that the man travelled while pillow's total journey
Therefore the total time for pillow to come back at the
same position from where it had been thrown down:
D = 16 feet
t = 16/8 = 2sec.
In two sec .....The distance travelled by man.
d1 = 0.8*2 = 1.6 feet
Now to get to more 1.6 feet it takes 0.22 sec.
Therefore the total time taken is 2.22 sec.
Hope you find it useful.
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Cheers!!!!!!!!@@@!!!!!!!!!
22 Sep 2007 14:26:13 IST
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@ Ayesha
The man wont be thrown with same velocity in opposite direction. Here masses of pillow and man are different. Apply Law of Conservation of Linear Momentum and see for yourself.
I mean to say is that the pillow has to travel a larger distance during ascent. SO time is larger..
The man wont be thrown with same velocity in opposite direction. Here masses of pillow and man are different. Apply Law of Conservation of Linear Momentum and see for yourself.
I mean to say is that the pillow has to travel a larger distance during ascent. SO time is larger..
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