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7 Feb 2007 22:08:31 IST

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Engineering Entrance , Medical Entrance , AIPMT , JEE Main , AIIMS , JEE Advanced , Physics , Mechanics

A bullet is dropped to the ground from the top of a building while another is fired towards the ground from the same building. Neglect air resistance, the acceleration is:

1)greatest for dropped bullet

2)greates for fired bullet

3)same for each

4)depends on how far they are from the ground.

[only one is correct.]

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sagarbhale

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7 Feb 2007 22:12:13 IST

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same for each i guess as they are both under the gravitational influence...the fired one will only have initial velocity and thus will reach the ground faster

am i correct??

ANIRUDH PEDAPROLU

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7 Feb 2007 22:16:23 IST

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hi Sagar,
i too had the same opinion but they key paper says that it is the (3)rd option. i.e. same for each

Anshuman Johri

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7 Feb 2007 22:19:45 IST

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The 3rd option is correct as the acceleration due to gravity g is the only accleration acting on both the bullets. So their velocities will be different but they always possess the same acceleration.

sagarbhale

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7 Feb 2007 23:10:33 IST

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aniruddh...thats what i said dident i???
SAME FOR BOTH!!!!!

Gautam sharma

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8 Feb 2007 00:12:39 IST

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it wd b the same

neil sabnis

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11 Feb 2007 23:58:02 IST

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its the same..because acc on the body in motion is always g downwards..so it dosnt matter wheather the body is goin up or down..the acc on each boy must remail g i.e the same......ryt anirudh???

Uday Prakash

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12 Feb 2007 13:31:21 IST

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how come it would be the same when u provide extra velocity to the bullet ?

remeber gravitation is the only retarding force

but in this case the fired bullet has acquired some velocity and the other has not

u may visualize it practically

fire a bullet and release the other

Shashank Ganesh

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12 Feb 2007 21:42:52 IST

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i think all of u are getting confused between the speeds and the accellerations of the bullet

the speeds are different..... accepted

but here we are being asked abt accelleration.

here accelleration would be the same fr both as gravity the only external force acting onthe bullets

neil sabnis

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12 Feb 2007 22:38:34 IST

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i think u day dude...u should again go through wht u hv written
acceletation is change in velocity...and not velocity..

sagarbhale

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13 Feb 2007 20:36:49 IST

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hi neil

uday use the basic defifnition of velocity.....it is CHANGE in velocity upon time and not just velocity

a = dv/dt or in other words a = v-u/t

thus the initial velocity is of no concern with the acceleration
try using the equation with examples mate you'll understand...or simply use deravitives if you know them

vash

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13 Feb 2007 20:58:38 IST

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i think it depends on the height. as the bullet is fired it attains a tremendous velocity in a short period of time. that means it has some initial acceleration. as it goes down it adds up to the natural g and keep on increasing till it reaches the ground. as in the second case it's just the 'g'. so it matters on the height from where they are fired. i think i am right, but if i am wrong then spot out my mistakes plzzzzzzzzzzzz........

goutham harsha (1nkZ)

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13 Feb 2007 21:07:18 IST

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C'mon, then explain this:

why don't we say that there might be another acceleration provided bcos of the force the gun exerts????????

sagarbhale

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13 Feb 2007 21:13:14 IST

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i did consider that possibility mate...but i don't think the problems means tht..it only means that one bullet has higher initial velocity and the other has the lower...tths how i interpret the problem...i don know about you guys...

if the force of gun is to be considered then the bullet fired from the gun will obiviously have higher acceleration as it has initial acceleration and it is fired in direction of the gravitational acceleration...the two will add up.

cheers!!

Anshuman Johri

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13 Feb 2007 21:13:59 IST

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kghedriu,

The force applied by the gun is impulsive and so it provides a certain momentum to the bullet. Once the bullet is fired there is no force exerted by the gun on the bullet. So the acceleration acting is only the acceleration dut to gravity. So the answer has to be c

sagarbhale

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13 Feb 2007 21:17:39 IST

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oh i c what you mean anshuman...perhaps you can elaborate mathematically so i'll understand better..please!!!

rohan sen sharma

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13 Feb 2007 23:39:59 IST

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well it is a damn simple ques.the only prob is that we r gettin confused betwn vel and acc.what johri said is absolutely correct.the gun gives an impulse to the bulletwhich is responsible for the initial vel.

but after that both the bullet travel under gravity.

so both are under same acc ie g.

001sri

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14 Feb 2007 12:25:45 IST

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same for both indeed.
the force u r taking of abt gun is an impulse so it impart only initial velosity n no acc.
close this chapter here.

vash

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14 Feb 2007 12:58:17 IST

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but it has some initial acceleration by the gun, the impulse and the acceleration can't be neglected. so there is an acceleration which continues thruout and adds upto g. so height matters. i think i only started the concept of the gun and perhaps i am only givin it a end. or mayn't be!!!!!!!!

Anshuman Johri

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14 Feb 2007 14:37:15 IST

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Hey vash,

Where in the world did u get the idea of initial acceleration of the bullet by the gun?

Impulse=Effect of force acting for a short interval of time=Change in momentum

=>I=

And dude, height dosent matter as only the acceleration is asked which has nothing to do with the height.

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