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Conservation of Energy
Work can be changed into potential or kinetic energy. If friction exists, work can be turned into internal energy.
Answer Me!!!
An average force of 20 N is used to pull the string of a bow equipped with an arrow back 0.60 m. When the arrow leaves the bow string after being released, how much kinetic energy does the arrow have?
Conservation of Energy
Energy cannot be created or destroyed. The total amount of energy of an object or system is a constant.
However, the energy can change forms between potential and kinetic.
Changing Work Into Energy
In a system with NO FRICTION, ALL OF THE WORK becomes potential or kinetic energy.
In a system that has friction, work must be done to overcome this force and will result in heat or internal energy.
Ideal Mechanical Systems
An Ideal Mechanical System is a system that has no friction or resistance.
All of the energy in an ideal mechanical system is comprised of potential and kinetic energy.
Nonideal Mechanical Systems A Nonideal Mechanical System is a system
that has some friction or other resistive (non-conservative) force.
Typically, non-conservative forces oppose motion and convert kinetic energy into heat energy.
Energy Conservation:Pendulum
Practice Problem 2
A 650 kg roller coaster starts from rest at the top of the first of three hills and glides freely. If the height of the three hills is 10 m, 6 m and 3 m respectively, find the kinetic energy at the top of the third hill.
Practice Problem 3
A 0.1 kg apple falls from a tree 2 m and hits a spring. If the spring is compressed 0.1 m from its rest position, what is the spring constant of the spring?
Practice Problem 4
A 0.1kg ball dropped vertically from a height of 1.0 m above the floor bounces back to a height of 0.8 m. How much mechanical energy is lost by the ball as it bounces?
Practice Problem 5
400 J of work is done to raise a 72 N box a vertical distance of 5 m. How much work is done to over come friction and air resistance?
Practice Problem 6
A 1.0 kg mass gains kinetic energy as it falls freely from a vertical distance d. How far would a 2.0 kg mass have to fall freely to gain the same kinetic energy?
