Homework Help: Explosion of firecracker on pond

1. Oct 15, 2012

omc1

1. The problem statement, all variables and given/known data A firecracker (mtot = 0.70 kg), sitting on a frozen pond, explodes into three pieces, each of which moves horizontally. Piece 1 (m1 = 0.20 kg; v1 = 100 m/s) moves at a right angle to piece 2 (m2 = 0.20 kg; v2 = 125 m/s). What is the speed of the third piece?

2. Relevant equations mv=p=j=ft

3. The attempt at a solution m(tot)v1+v2+v3=ft i think t=v(final)/a and a would be equal to gravity but iam just not sure. thanks for help!

2. Oct 15, 2012

tiny-tim

hi omc1!
what is this supposed to be?

what principle do you think applies here?

(and what topics have you been lectured about this week?)​

3. Oct 15, 2012

omc1

we have only talked bout impulsion and momentum so far i think thurseday we begin collision....

4. Oct 15, 2012

omc1

the formula applies to mas total times the sum of the velocities is the force times time....

5. Oct 15, 2012

tiny-tim

an explosion is a type of collision (in reverse!)

what happens to momentum in a collision?

(and do you need to answer this before thursday?!)

6. Oct 15, 2012

omc1

momentum is conserved in a collision, yes my hw is due wednesday night.

7. Oct 15, 2012

tiny-tim

ok, the initial momentum is zero

(because the question says the firecracker is "sitting")

sooo … ​

8. Oct 15, 2012

omc1

mmmm ok so m(tot)v1+v2+v3=0 iam not sure

9. Oct 15, 2012

tiny-tim

no, that's multiplying the total mass by the sum of the velocities

you need to add the individual momentums (ie individual mass times individual velocity)

10. Oct 15, 2012

omc1

soo m1v1+m2v2+m3v3=0 ??

11. Oct 16, 2012

yup!