IGCSE/GCSE/O & A Level/IB/University Student Forum

Qualification => Subject Doubts => GCE AS & A2 Level => Sciences => Topic started by: xim7007 on August 25, 2010, 12:12:49 pm

Title: Collisions in two dimensions problem (urgent)
Post by: xim7007 on August 25, 2010, 12:12:49 pm

A shell of mass 12kg moving horizontally at 320m/s explodes into three fragments A, B and C,
which continue to move in a common vertical plane.

Fragment A: mass= 2kg, speed= 450m/s, 45degree above the horizontal
Fragment B: mass=6kg, speed=400m/s, moves horizontally
Fragment C: mass=m, speed=v, in a direction teta to the horizontal

Calculate the size of the momentums of the shell before it explodes and of fragments A and B
afterwards.  :) help me...

Title: Re: Collisions in two dimensions problem (urgent)
Post by: Deadly_king on August 25, 2010, 01:24:35 pm

well momentum is the product of mass and linear velocity.

so for the shell.......momentum = 12*320 = 3840 Ns

You need to find the component of velocity along the horizontal plane since momentum requires value for linear velocity. So fragment A : p = 2*(450cos45) = 636.4 Ns

Fragment B : p = 6*400 = 2400

If you the apply the law of conservation of momentum you can find the momentum of fragment C too.

p = 3840 - (2400+636.4) = 803.6 Ns

Hope i've been able to help you. If u dont understand do ask.......i'll try to make myself clearer

Title: Re: Collisions in two dimensions problem (urgent)
Post by: Alpha on August 25, 2010, 01:59:30 pm

Thank you for helping Deadly_King. +rep. :)

Title: Re: Collisions in two dimensions problem (urgent)
Post by: Deadly_king on August 25, 2010, 02:13:45 pm

hehe.........its alright!!

i told you......i love to help others........i just hope that i've made myself clear enough!

Title: Re: Collisions in two dimensions problem (urgent)
Post by: Alpha on August 25, 2010, 02:17:56 pm

Sure enough. :)

Title: Re: Collisions in two dimensions problem (urgent)
Post by: Deadly_king on August 25, 2010, 02:25:27 pm

really??
dont tell me you uinderstood that :P

+rep

Title: Re: Collisions in two dimensions problem (urgent)
Post by: Alpha on August 25, 2010, 02:28:29 pm

Quote from: Deadly_king on August 25, 2010, 02:25:27 pm

really??
dont tell me you uinderstood that :P

+rep

I can at least pretend.  :P

Title: Re: Collisions in two dimensions problem (urgent)
Post by: Deadly_king on August 25, 2010, 02:40:24 pm

hehe.......thats very sweet of ya :)

thanks......its really encouraging :)

Title: Re: Collisions in two dimensions problem (urgent)
Post by: Alpha on August 25, 2010, 02:43:07 pm

Quote from: Deadly_king on August 25, 2010, 02:40:24 pm

hehe.......thats very sweet of ya :)

thanks......its really encouraging :)

You're welcome. =)

Title: Re: Collisions in two dimensions problem (urgent)
Post by: xim7007 on August 25, 2010, 07:17:49 pm

Thanks guys. I also got the same answers as yours but in the answer key it's a different story. In the answer key it's given:

Before explosion, momentum of shell=12 kg × 320 m/s
= 3840 kg m/s
After explosion, momentum of A = 2.0 kg × 900 m/s
=1800 kg m/s
and momentum of B = 6.0 kg × 420 m/s
=2520 kg m/s

Can anyone explain this?

Title: Re: Collisions in two dimensions problem (urgent)
Post by: Deadly_king on August 29, 2010, 11:39:57 am

sorry.....cant figure it out!

but if you take a close look at its answers we can note that it does not obey the law of conservation of momentum. So my conclusion is that the shell must have hit some other moving object upon explosion.

May i know from where you got this question?.....i would really like to take a closer look if possible :)