Laws of Motion
Conservation of Momentum
previous | next
Let us take two
bodies say two balls. We assume that these balls are
in a place where no external forces are acting on
them. Such a place would be called an isolated
system. Let one ball be moving along a straight
line with velocity v1 and let the other
ball be moving with a velocity v2. Now
these velocities are different. So, as both balls are
moving along the same line, they will hit each other
at some point of time if the ball, which is following
is moving at a faster speed. If you were to walk
exactly behind some one, and walk faster than, you
will run into this person ahead of you if you do not
take evasive action!
After the
collision the balls will move with new velocities v1'
and v2'. What is the relation between the
way the balls move before and after the collision?
The answer lies
in the law of conservation of momentum
Law of
conservation of momentum: In the absence
of external forces, the total momentum of the system
is conserved.
So using this
law we can write the following equation about the two
colliding balls, having mass m1 and m2.
m1v1
+ m2v2
= m1v1'
+ m2v2'
This is a very
neat and a universally applicable law. It is true
whether the balls are planets! or atoms!
A shell of mass
0.020 kg is fired by a gun of mass 100 kg. If the
muzzle speed of the shell is 80 m/s, what is the
recoil speed of the gun?
Let m and v be
the mass and velocity of the shell and M and V the
mass and velocity of the gun.
V = mv/M
=0.020 x 80/100
= 0.016 m/s
|
