Lecture 4 - Work and Energy

Work

when a force moves an object through a certain distance we say work is accomplished

Force can be displayed in the horizontal and vertical

vertical = F sin theta

horizontal = F cos theta

Work = Fd cos/sin theta

mew k

the kinetic coefficient of friction , it represents the ratio of the force of friction between two bodies to the normal force pressing them together.

Force formula when friction is present

frictional force (f) = mew k X m X a

Force - frictional force = 0

therefore Force = frictional force

example: what is the maximum work needed to push a 950 kg car 810m up a 9 degree incline?

example: what is the maximum work needed to push a 950 kg car 810m up a 9 degree incline WITH FRICTION OF 0.25

What is energy

the ability to do work

What is kinetic energy

the energy of an object by virtue of its motion

what is potential energy

the energy of an object by virtue of its position or configuration

gravitational potential energy = mgh

Elastic potential energy = 0.5kx²

Energy Principle

A net force accelerates an object from v initial to v final over a displacement d

Therefore, net work done on an object is equal to change in its kinetic energy

conservation of mechanical energy

total mechanical energy E of a system remains constant = Kinetic initial + Potential initial

Conservation of mechanical energy equation

KE(f) + PE(f) = KE(i) + PE(i)

What is power

the time rate of doing work