# 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

### tiny-tim

yup!

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