PHY - work and power

definition of energy

Energy is the ability to do work

what is energy measured in

Joules

what is the equation for work done

work done = force/ distance moved in direction of force

W = Fd

definition of a joule

one joule is the work done when a force of one newton moves an object one meter

whats the equation for work done against gravity

W = mgh

mass - Kg

gravity - 9.81

height - meters

what is the equation for GPE

GPE = mgh

where does the small amount energy lost when a ball falls back to earth go

elastic - when it hits the ground

thermal

sound

what is the equation for Kinetic Energy

KE = ½ mv²

describe the transfer between KE and GPE energy stores when a ball is thrown vertically upwards

• at the star the ball has no GPE only KE, which is at its Max.

• By the time the ball reaches the top of its flight all the KE has been transferred to GPE

• as the ball is midway falling back down the GPE is slowly transferred back into KE

• Just as it hits the ground the ball has Max. KE and 0 GPE

• it then looses a small amount of energy to thermal (+ elastic potential and sound)

how do you relate GPE to KE

GPE = KE

mgh = ½ mv²

h = v²/ 2g

v = √2gh

describe the path of a golf ball in terms of energy

• at beginning KE = max

• at the top of the flight the KE is less than at the beginning and GPE is at its max.

• if you want to find KE as the highest point it is initial KE - GPE at the top

what is the equation for power

power = energy/time

P = E/t

note energy = work done

what is the unit of power

Watts

W