Inertia and Momentum
- Inertia is the tendency of an object to remain in its current state of motion - at rest or moving at a constant velocity.
- Inertia depends only on an object’s mass thus an object's inertia cannot change.
- Momentum is the tendency of a moving object to maintain its current velocity. The greater the momentum, the greater the unbalanced force needed to change the object's motion.
- Momentum depends on both an object's mass and velocity thus momentum of an object changes with a chang in its velocity.
- Momentum is a vector quantity (involves direction as well as magnitude)
- Momentum = mass x velocity
- Units Ns or kg m/s
See useful web sites on momentum and Inertia
Extension Motion Questions
These problems may be solved by a combination of the basic motion formulae used within your booklet or you may apply the extension formulae at the back of your booklet.
These formulae will be given to you in your exam if they are required to solve any problems
v = u + at
s = ut + ½ at2
v2 = u2 + 2as
Where u = initial velocity or v1 and v = final velocity of v2
Example:
(a) Find the time taken for an object to drop 20 m from a high rise building. and
(b)Find the object's final velocity.
Answer:
(a) Suitable formulae
s = ut + ½ at2
Substituting into formulae
20 = 0 x t + ½ x 9.8 x t2
20 = 4.9 x t2
t2 = 20/4.9 = 4.1
t = 2.02 s
(b) Suitable formulae
v = u + at
Substituting into formulae
v = 0 + 9.8 x 2.02
v = 19.9 m/s
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Data:
u = 0 m/s (v1)
a = 9.8 m/s2
s = 20 m
t = ?
v = ? (v2)
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