Chapter 5 Flashcards
(14 cards)
Does work have a direction?
Can it be negative or positive?
What is it’s units?
Does not have a direction
Can be negative or positive depending on value of cosθ
Joules (J)= 1N•m = 1kg•m/s^2
Work is only don’t parallel to displacement!!!!
If two masses are connected and remain at fixed distances from eachother, how do you find the net external force on them?
ΣFext=(Σmi)asys
Mass internal (added masses together)
Acceleration of system
If a string using gravity is pulling a box by a pulley on a frictionless surface, will the acceleration be equal to the acceleration due to gravity?
No the acceleration will be less than the acceleration due to gravity always
How are work and kinetic energy related?
The net work done on an object is equal to the change in the objects kinetic energy
What is a conservative and nonconservative force?
What is the equation connecting them?
Conservative- work done by force in moving an object between two points is the same no matter which path is taken
Can be easily recovered
Nonconservative- dissipative- randomly disperses energy of objects
Can’t be easily recovered
Went=Wc+Wnc=ΔKE
Wc=-ΔPE
Mechanical energy is changing if work is being done by a non conservative force
What kind of force is gravity?
Conservative
What is the equation for potential energy with gravity?
PE=mgy
Wc=mgyi-mgyf=PEi-PEf
How do the initial potential energies and the final potential energies relate?
KEi+PEi=KEf+PEf
1/2mvi^2+mgyi=1/2mvf^2+mgyf
How does the mechanical energy in an isolated system of objects interacting through conservative forces change over time?
It remains the same at all times
What is hookes law with springs?
Fs=-kx
Fs- force exerted by the movable end of spring
X- position x
Spring force is conservative
How can work be found on a Force vs displacement graph?
It’s the area under the line
What is the equation for work done by an ideal spring?
W=-1/2 KXf^2
What is elastic potential energy?
Potential energy stored in a spring
ΔPEs=-Wspring
ΔPEs=1/2 kxf^2-1/2kxi^2
PEs=1/2kx^2
What is power?
Rate at which energy is transferred
Rate if doing work
P=W/Δt=FΔx/Δt=Fv
J/s (Watt) W
