Physics Flashcards
When is work done on an object?
When a force causes a displacement of the object
The force must be _____ to the displacement to do work.
Parallel
If a student carries a bucket of water along a horizontal path while walking at constant velocity, what work is done?
0 because the force required to keep the bucket up is perpendicular to the horizontal displacement of the bucket.
If there are many forces acting on an object, how do you find net work?
Wnet = Fnet * d * cos(angle)
When is work positive?
When the direction of the force applied and displacement is the same. Speed gets bigger.
When is work negative?
When the direction of the force , such as kinetic force, and displacement are opposite. The speed slows down.
Kinetic energy
Associated with motion; m(v^2)2
Net work done by a net force is equal to change in
kinetic energy
Potential energy
is associated with an object that has the potential to move because of its position relative to some other location
Gravitational potential energy
PE= mgh
As an egg falls of a table, what are the energy conversions?
PE to KE
Elastic potential energy depends on
distance compressed or stretched
What is stored in a spring if an external force compresses or stretches it?
Elastic potential energy
Elastic potential energy formula
PEelastic = 0.5k(x^2)
When is k small? big?
Small if spring very flexible and big if spring is stiff
At the highest point in its path, what type of energy does a pendulum have the highest of?
Gravitational potential energy
At its lowest point, what type of energy does a pendulum have the most of?
Kinetic energy
Mechanical energy
Sum of kinetic and all forms of potential energy
ME = KE + PE
Conservation of mechanical energy
In the absence of friction, mechanical energy stays constant althouhg KE and PE can interconvert.
Power
W/t or rate of energy transfer.
What type of function is work?
A path function which means it depends on path taken
When is work a state function? and why?
In a gravitational field, work is independent of the path taken because only force acting is gravity and therefore work will depend on vertical distance traveled.
When an object is lifted to a certain height, what type of energy is the work equal to at that height?
Gravitational potential energy or W=mgh
Work done against gravity is equal to
mgh
If there is centripetal force and an object moves in a circular path, what is the work?
It is zero because displacement and force are perpendicular to eachother
A student holds a 10kg stack of books 1.5m above the ground for 20s. How much power was used to hold the books during this time?
Power is given by P=W/t=F→⋅d→/t. Although the student exerts a force on the books during this time, they are not moved at all, so the displacement d is 0, and thus the power is also 0.
