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Learning Outcome :

 Define the momentum of an object
 Define momentum (p) as the product of mass
( m) and velocity (v), e. p=mv
 State the principle of conversation of
momentum
 Describe applications of conservation of
momentum.

 Momentum is a commonly used term in sports
 A team that has the

 The momentum of an object is the product of
the mass and the velocity of the object

 Situation 1
 Car A and car B have
the same mass but
they move with
different velocities.
 Which car possess
more momentum?

 Situation 2
 The lorry and the
car move with the
same velocity but
they have different
masses.
 Which vehicle
possess more
momentum ?

The principle of conservation of momentum
states that in a system make out of
objects that react (collide or explode), the
total momentum is constant if no external
force is acted upon the system.

Sum of Momentum Before Reaction = Sum of Momentum After Reaction

Formula of Principle of Conservation of
Momentum

Example : Both objects are same direction before
collision
A Car A of mass 600 kg moving at 40 ms-1
collides with a car B of mass 800 kg moving
at 20 ms-1 in the same direction. If car B
moves forwards at 30 ms-1 by the impact,
what is the velocity, v, of the car A
immediately after the crash?

m1 = 600kg m2 = 800kg
u1 = 40 ms-1 u2 = 20 ms-1
v1 = ? v2 = 30 ms -1

Answer :

According to the principle of conservation of
momentum,
m1u1 + m2u2 = m1v1 + m2v2
(600)(40) + (800)(20) = (600)v1 + (800)(30)
40000 = 600v1 + 24000
600v1 = 16000
v1 = 26.67 ms-1

Example 2 : Both objects are in opposite direction
before collision

A 0.50kg ball traveling at 6.0 ms-1 collides head-on
with a 1.0 kg ball moving in the opposite direction at
a speed of 12.0 ms-1. The 0.50kg ball moves
backward at 14.0 ms-1 after the collision. Find the
velocity of the second ball after collision.
m1 = 0.5 kg
m2 = 1.0 kg
u1 = 6.0 ms-1
u2 = -12.0 ms-1
v1 = -14.0 ms-1
v2 = ?

(IMPORTANT: velocity is negative when the object move
in opposite siredtion)

Answer :

momentum,
m1u1 + m2u2 = m1v1 + m2v2
(0.5)(6) + (1.0)(-12) = (0.5)(-14) + (1.0)v 2
-9 = - 7 + 1v 2
v2 = -2 ms-1

Elastic collision is the collision where the kinetic
energy is conserved after the collision.

Total Kinetic Energy before Collision
= Total Kinetic Energy after Collision

Additional notes:
-In an elastic collision, the 2 objects
separated right after the collision, and
-the momentum is conserved after the
collision.

Inelastic collision is the collision where the
kinetic energy is not conserved after the
collision.

Additional notes:
-In a perfectly elastic collision, the 2 objects
attach together after the collision, and
-the momentum is also conserved after the
collision.

 Example 3 : Perfectly Inelastic Collision

A lorry of mass 8000kg is moving with a
velocity of 30 ms-1. The lorry is then
accidentally collides with a car of mass
1500kg moving in the same direction with a
velocity of 20 ms-1. After the collision, both
the vehicles attach together and move with a
speed of velocity v. Find the value of v.

momentum,
m1u1 + m2u2 =( m1+ m2) v (8,000)
(30) + (1,500)(20) = (8,000)v+ (1,500)v
270,000 = 9500v
v = 28.42 ms-1

Answer:
(IMPORTANT: When 2 object attach together,
they move with same speed.)

Application of Conservation of Momentum

: Jet Engine •The hot gas is forced
through the engine to
turn the turbine
blade, which turn
the compressor.
• High-speed hot gases are
ejected from the back with
•Air is taken in from the front and is high momentum. This
compressed by the compressor. produces an equal and
•Fuel is injected and burnt with the opposite momentum to push
compressed air in the combustion the jet plane forward.
chamber.

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2.4 analysing momentum

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