Chapter 7
Momentum and Collisions
Linear
Momentum
Momentum
is the mass times velocity.
SI
unit:
Example
71
(a)
A 1180 kg car drives along a city street at 30.0 mph (13.4 m/s).
What is the magnitude of the car's momentum?
Solution:
(b)
A major league pitcher can give a 0.142 kg baseball a speed of 101
mph (45.1 m/s). Find the magnitude of the baseball's momentum?
Solution:
Example
72
The
figure shows a 2.0 kg toy race car before and after taking a turn
on a track. Its speed is 0.50 m/s before the turn and 0.40 m/s after
the turn. What is the change in
the linear momentum of the car due to the turn?
Solution
Impulse
and Momentum Change
The
Law of Conservation of Momentum
If no net
external force acts on objects in a system, the total linear
momentum of
the system cannot change.

Newton's Second Law was written in momentum form at first.
Newton's Second Law
The time rate change of the momentum of a particle is
equal to the net force acting on the particle and is in
the direction of that force.

Example 73
The figure gives
the linear momentum versus time for a particle moving along
an axis. A force directed along the axis acts on the particle.
(a) Rank the four regions indicated according to the magnitude
of the force, greatest first. (b) In which region is the particle
slowing?
Solution
Example 74
At
a city park, a person throws some bread into a duck pond. Two
4.00 kg ducks and a 9.00 kg goose paddle rapidly toward the
bread, as in the figure. If the ducks swim at 1.10 m/s, and
the goose swims with a speed of 1.30 m/s, find the magnitude
and direction of the total momentum of the three birds.
Solution
Impulse 