MOMENTUM
Momentum can be defined as "mass in motion." All objects have mass; so if an object is moving,
then it has momentum - it has its mass in motion.
Momentum depends upon the variables mass and velocity. Thus the greater an object's mass or
the greater its velocity, the greater its momentum. In terms of an equation, the momentum of an
object is equal to the mass of the object times the velocity of the object.
Momentum = mass X velocity
In physics, the symbol for the quantity momentum is the lower case p. Thus, the above equation
can be rewritten as
p=mXv
where m is the mass and v is the velocity.
The units for momentum would be mass units times velocity units. The standard metric unit of
momentum is the kgm/s.
Momentum is a vector quantity. As discussed in an earlier unit, a vector quantity is a quantity
that is fully described by both magnitude and direction.
Momentum Triangle
WORKED EXAMPLES
1. Calculate the momentum of a 1200kg car with a velocity of 25m/s.
Solution:
Mass, m = 1200kg
Velocity, v = 25 m/s
Momentum, p = m x v
p = mv = 1200 X 25 = 30,000kg.m/s
2. What is the momentum of a child and wagon if the total mass of the child and wagon is 22kg
and the velocity is 1.5m/s?
Solution
Mass= 22kg
Velocity = 1.5 m/s
Momentum, p = m x v
p = mv = 22 X 1.5 = 33kg.m/s
3. The parking brake on a 1200kg automobile has broken, and the vehicle has reached
a momentum of 7800kg.m/s. What is the velocity of the vehicle?
Solution:
Mass = 1200kg
Momentum, p = 7800 kgm/s
V = p/m = 7800/1200 = 6.5m/s
Law of conservation of momentum
The law of conservation of momentum states that the momentum of an isolated system remains
constant.