The Law of momentum conservation also applies to explosion.
Do you mean
explosion as in bomb explosion? Yes. Explosion is the reverse of
collision. If you video tape an explosion and play it backwards, it looks like a
collision. Likewise, if you video tape a collision and play it backwards
it resembles an explosion. Let's look at some
examples of explosion, like, gun shooting, cannon bombing and rocket launching.
Can you name some other examples of explosion that is happening around you?
Gun shooting
Imagine a bullet being fired from a gun. What is the momentum of the system before firing? 0, of course! Because there is no movement before the firing. Then what is the total momentum after firing? 0 again, of course! Simply because of the Law of Momentum Conservation.
A bullet of 10 g was fired from a gun that is 490 g. After firing, the bullet flew out at 20 ms-1 , calculate what is the velocity of the gun.
| Momentum before firing | Momentum after firing | ||
| Gun | Bullet | Gun | Bullet |
| 0 | 0 | 0.49 x v | 0.01 x 10 = 0.1 |
|
Total momentum before firing |
= | Total momentum after firing |
| 0 kgms-1 | = | (0.49v + 0.1) kgms-1 |
| 0.49v | = | -0.1 |
| v | = | -0.2ms-1 |
(negative velocity means the gun moves opposite direction to the bullet, the shooter is bounced backward).
Cannon bombing
When TNT is lighted, an explosion force the ball out of the cannon with 40 ms-1 while the cannon is pushed back by another force. These two forces are equal in size but opposite in direction. Momentum is conserved. What is the velocity of the cannon? Click here to find out. (External forces have been removed by placing the cannon on a frictionless surface).
Last updated: 16 Sep 2002