Post on 10-Apr-2015
AP Phys BTest Review
Momentum and Energy
4/28/2008
Overview
Momentum• Center of Mass
• Impulse-Momentum Theorem
• Conservation of Momentum
Energy• Work-Energy Theorem
• Conservation of Energy
• Elastic and Inelastic Collisions
Momentum
Momentum• Momentum is defined as:
• The rate of change of momentum of an object is equal to the net force applied to the object.
p m v
F
p
t
Conservation of Momentum
Conservation of momentum states that: the total momentum of an isolated system of objects remains constant.• Isolated system: no outside forces acting on
the system
• Tip: Break the momentum of each component up into horizontal and vertical components: these are independent of one another!
Collisions and Impulse
Impulse-momentum theorem defines impulse and says that the impulse on a system will be equal to the change in its momentum. F t p
Center of Mass
The center-of-mass of a collection of particles if given by the following equation:
• The total linear momentum of a system of particles is equal to the total mass M of the system multiplied by the velocity of the center of mass of the system.
• Extended systems use this formulation for Newton’s Laws too.
xM
m xCM i i1
Work and Energy
Work is merely a force applied on an object over a certain distance.
Kinetic Energy is the energy of motion.
Potential Energy is the ability of an object to start/stop motion.• Gravity: Elastic
W Fd cos
T m v1
22
U mgh U kx1
22
Work-Energy Theorem
This principle states that the work done on an object is equal to the change in kinetic energy of an object
W T
Conservation of Energy
Conservative vs. Non-conservative Forces• Friction
Conservation of Energy: The total energy of an isolated system cannot change.• Shift between potential and kinetic energy.
Power
Power is defined as energy over a given time period.
Collisions
Elastic Collisions• “Rubber” – things bounce off.
• Both energy and momentum are conserved.
Inelastic Collisions• “Gluey” – things stick together
• Only momentum is conserved!
Rotational Mechanics
Radians Angular displacement, velocity,
acceleration Moment of Inertia Torque Angular Momentum
Simple Harmonic Motion
Period and Frequency Oscillatory Motion
• Springs, Pendulums
• Conservation of Energy
• Position as a function of time
x t A t( ) cos( )