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SUDESHNA
PAUL EDUCATIONAL COMPANION

INERTIA & MOMENTUM

Trains
Collision
Conservation of
momentum

Head-on Collision Two Cars Collision
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Physics

The law of
inertia is most commonly experienced when riding in cars and
trucks. In fact, the tendency of moving objects to continue in motion is a
common cause of a variety of transportation accidents - of both small and large
magnitudes.

Trains Collision

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Conservation of momentum

The collision
between a 3.0-kg loaded cart and a 2-kg dropped brick. It will be assumed that
there are no net external forces acting upon the two objects involved in the
collision. The only net force acting upon the two objects (loaded cart and
dropped brick) are internal forces - the force of friction between the loaded
cart and the droped brick. The before- and after-collision velocities and
momentum are shown in the data tables.

Head-on Collision

n the collision between the truck and the car,
total system momentum is conserved. Before the collision, the momentum of the
car is +20 000 kg*m/s and the momentum of the truck is -60 000 kg*m/s; the total
system momentum is -40 000 kg*m/s. After the collision, the momentum of the car
is -40 000 kg*m/s and the momentum of the truck is 0 kg*m/s; the total system
momentum is -40 000 kg*m/s. The total system momentum is conserved. The momentum
change of the car (-40 000 kg*m/s) is equal in magnitude and opposite in
direction to the momentum change of the truck (40 000 kg*m/s) .

Two Cars
Collision

When considering the total momentum of the system
before the collision, the individual momentum of the two cars must be added as
vectors. That is, 20 000 kg*m/s, East must be added to 10 000 kg*m/s, North. The
sum of these two vectors is not 30 000 kg*m/s; this would only be the case if
the two momentum vectors had the same direction. Instead, the sum of 20 000
kg*m/s, East and 10 000 kg*m/s, North is 22 361 kg*m/s at an angle of 26.6 North
of East. Since the two momentum vectors are at right angles, their sum can be
found using the Pythagorean theorem Go to the top