Work, Energy, Power and Momentum Flashcards
When looking at change in momentum problems
Pay attention to the direction of velocity
If work is performed by a net force
W= ΔKE
Formula for weight
W = mg
Formula for Potential Energy
PE = mgh
When approaching an elevator problem where you’d feel lighter
Subtract acceleration to gravity
Hooke’s Law
F = -kx
Formula for force of gravity
Fg = F (m1m2/r^2)
Which situations should be treated as elastic collisions
If objects bounce off each other during collisions
Static Friction
Object is not moving
What kind of work is done when an object moves up
Negative, against gravity
Newton’s second law
Sum of the forces always equals m*a
Elastic Potential Energy Formula
P.E.e = 1/2kx^2
Formula for Work
W=Fdcosθ
Units for Work
J/Kgm/Kgm^2/s^2
Impulse
The product of the force and the time for which the force is applied
What kind of work is done when holding stationary objects?
No work is done when holding stationary objects. Without displacement work done is zero
Both masses united by one rope will have the same acceleration and tension
Find out which force wins and calculate the acceleration using their combined masses.
This does not work for tension
Elastic Collisions
Both the momentum and the kinetic energy are conserved.
Inellastic Collisions
Total kinetic energy of the system is not conserved
When friction is ignored the total mechanical energy in a system
Remiains the same
What is the relationship between mass and velocity
The speed of a falling object is not dependent upon its mass. We don’t need to know the mass to determine the final velocity
Formula’s for Impulse
FΔt = Δp or FΔt = mΔv or FΔt = m(vf – vi)
How does the momentum of an object change
Anytime its velocity or mass changes
Formula’s for Power
P= (W/t) = (fd/t) = fv
Linear momentum
p=mv
Conservation of Momentum general formula for two objects
m1v1i + m2v2i = m1v1f + m2v2f
Newton’s third law
For every force exerted by one bisect on a second object, there is an equal but opposite force by the second object
What happens to the Normal force when you press down on an object
It increases since there is more friction
Newton’s first law
An object’s velocity remains constant unless a force is acting upon it
If the sum of the forces equals zero then velocity is constant
Mechanical Energy is conserved if
No work is done by no conservative force (friction, air resistance, etc.)
Formula for Mechanical Energy
E = KE + PE
If work is performed by none conservative forces
Wnc = ΔE
For questions that ask you to calculate the change in momentum of a single object, where the mass of the object does not change use
Δp = pf – pi = mvf – mvi = m(vf – vi)
Centripital force formula
Fc = (mv^2/r) = mac
Formula for Gravitational Potential Energy
P.E. = mgh
When on a horizontal plane the normal force and weight will
Equal each other.
Not the case on an incline plane
Because mechanical energy in a system is conserved in problems where you are given a few known variables
You can set P.E. = K.E.
Mechanical Energy
The sum of the kinetic energy and all forms of potential energy in the system
Formula for Kinetic Energy
KE = 1/2(mv^2)
When apporaching an elevator problem where you’d feel heavier
Add acceleration to gravity
Which situations should be treated as inellastic collisions
Objects remain in contact after the collision
Centripial acceleration formula
ac = (v^2/r)
What relationship does the force an object experiences have towards the time that force acts
It’s inversely proportional.
i.e. That means that if it takes longer for an object to come to a stop, it will experience a smaller instantaneous force
Formula for force of friction
Ff = μN
Kinetic Friction
Object is sliding accross the surface
