Ch 6 Impulse & Momentum

This unit will put all of our previous knowledge of motion and energy together! Keep Newton's Laws and the ideas of
conservation of energy in mind when trying solve problems later in this chapter.

Be sure to check out the Physics Classroom's tutorials and interactives on Momentum


animated gif from The Physics Classroom


This is the 'fat mom" part of momentum... Force x time = change in momentum
J = Ft = change in momentum


A 1000kg car is traveling east at 25m/s. An impulse of 4000Ns in the same direction of motion is given to the car. What is the car's final velocity?
Initial momentum + Impulse = final momentum
initial mv + J = final mv
(1000kg)(25m/s) + 4000Ns = 29000kgm/s east

final velocity = final momentum / mass
v = (29000kgm/s) / (1000kg) = 29 m/s east

Conservation of Momentum

Momentum is also a vector and is ALWAYS conserved no matter what the situation. It is important to define what the system is that will
be examined and consider the initial and final momentums of the system as a whole. The system in the animation above is the truck AND the car.
The total initial momentum is the sum of the initial momentums of each vehicle BUT... be sure to keep in mind one is negative while the other is
positive since they point in opposite directions! The total momentum of the system is conserved while the pieces inside the system can change.
Total momentum of system = (2kg)(5m/s) + (5kg)(0m/s)
Total initial momentum = 10 kgm/s to the RIGHT
Total FINAL momentum of system = 10kgm/s to the RIGHT
Total final momentum = -(2kg)(10m/s) + (5kg)(?)
Solve for unknown velocty
10 kgm/s = -20kgm/s (LEFT) + (5kg)V (RIGHT)
30 kgm/s = (5kg)V
V = 6m/ the Right

Explore Conservation of Momentum in Collisions

Select ONE dimension to start...

Car Crash Physics

Hyperphysics Seat Belt Physics