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Mechanics

Blazing goIITian

 Joined: 11 Feb 2007 Post: 435
13 Feb 2007 15:37:25 IST
0 People liked this
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BITS PILANI QUESTION
Engineering Entrance , Medical Entrance , AIPMT , JEE Main , AIIMS , JEE Advanced , Physics , Mechanics

two bodies a and B r thrown upward simultaneously with the same speed.The mass of A is greater then that of B.Suppose the air resistance is equal for both of them and the air exert a force then

(a)The two bodies will reach the same height
(b)A will go higher than B
(C)B will go higher than A.
(D)none of these

Cool goIITian

Joined: 10 Jan 2007
Posts: 49
13 Feb 2007 22:00:23 IST
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without the air resistance they would have reached the same height as the accl. of both would have been equal to g(in downward direction).
but in this case in addition to gravitational force resistive force is also acting which is equal in magn. for both thus as the mass of A is greater therefore its accl. would be lesser than that of B in downward direction. thus A will go higher than B

Blazing goIITian

Joined: 7 Feb 2007
Posts: 544
13 Feb 2007 22:20:25 IST
1 people liked this

Effect of gravity is constant for both. Hence, the effect should be caused by resisting force. As m is inversely proportional to a when F is constant, we can say easily that A rises higher than B
Anyway, thanks for ur question

New kid on the Block

Joined: 14 Feb 2007
Posts: 8
14 Feb 2007 01:38:01 IST
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applying energy conservation ,both the bodies will reach the same height.

Scorching goIITian

Joined: 28 Dec 2006
Posts: 205
14 Feb 2007 12:16:44 IST
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A will go higher as acc due to air resistance is less for A(large mass same force) and acc due to gravity is same for both.

Cool goIITian

Joined: 13 Sep 2007
Posts: 96
7 Oct 2007 12:34:19 IST
1 people liked this

see deep, here the initial velocity is same therefore

v^2 - u^2 = 2as
v = 0 for both
u = same for both
a = -g forboth

therefore the height will be same for both when there is no resistance.

also as per we consider forces

since mass of a is larger so force given to A is larger ( but the velocity is same thus g make the same effect on both) also the force feel by A is larger. If we take effect of gravitational force in terms of speed then it will reduce the same as it reduce the speed of B. (due to difference in initial forces of A and B) so the effect on height is only due to initial velocity not by forces if we not consider the resistance.

But when we consider the resistance which is same for both A and B then

R = m * a
where a is retarding acceleration.
as mass of a is larger the retardation a is lesser so B will feel relatively more effect on velocity than a so A will go above than B.

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