EXAM GUIDELINES P1
Momentum and Impulse
(This section must be read in conjunction with the CAPS, p. 99–101.)
Momentum
- Define momentum as the product of an object's mass and its velocity.
- Describe the linear momentum of an object as a vector quantity with the same direction
as the velocity of the object.
- Calculate the momentum of a moving object using:
p = mv.
- Describe the vector nature of momentum and illustrate it with some simple examples.
- Draw vector diagrams to illustrate the relationship between the initial momentum, the
final momentum and the change in momentum for each of the above examples.
Newton's second law of motion in terms of momentum
- State Newton's second law of motion in terms of momentum: The resultant/net force
acting on an object is equal to the rate of change of momentum of the object in the
direction of the resultant/net force.
- Express Newton's second law of motion in symbols:
- Calculate the change in momentum when a resultant/net force acts on an object and its
velocity:
- Increases in the direction of motion, e.g.2nd stage rocket engine fires
- Decreases, e.g. brakes are applied
- Reverses its direction of motion, e.g. a soccer ball kicked back in the direction it
came from
Impulse
- Define impulse as the product of the resultant / net force acting on an object and the time
the resultant/net force acts on the object.
- Deduce the impulse-momentum theorem:
- Use the impulse-momentum theorem to calculate the force exerted, the time for which
the force is applied and the change in momentum for a variety of situations involving
the motion of an object in one dimension.
- Explain how the concept of impulse applies to
safety considerations in everyday life,
e.g. airbags, seatbelts and arrestor beds.
Conservation of momentum and elastic and inelastic collisions
- Explain what is meant by a closed (an isolated) system
(in Physics), i.e. a system on
which the resultant / net external force is zero.
A closed (an isolated) system excludes external forces that originate outside the colliding
bodies, e.g. friction.
Only internal forces, e.g. contact forces between the colliding objects, are considered.
- State the principle of conservation of linear momentum: The total linear momentum of a
closed system remains constant (is conserved).
- Apply the conservation of momentum to the collision of two objects moving in one
dimension (along a straight line) with the aid of an appropriate sign convention.
- Distinguish between elastic collisions and
inelastic collisions by calculation.