# Concept of work done

1. Sep 30, 2009

### MechaMZ

An object is moving with an initial velocity 5m/s, if i'm applying a force against it and it stops after a displacement.

So the work done is equal to 0.5m(0)2-0.5m(5)2

A stationary object, 0m/s, if i'm applying a force to it and it moves with a velocity of 5m/s, and stop after the force removed.

So the work done is equal to zero? 0.5m(0)2-0.5m(0)2=0
Should it be zero? and why it is zero? the object did travel a distance isn't?

definition: Work is a measure of change of energy.
So does it mean no matter how far an object moved, or how fast it has moved, we only consider the initial velocity and final velocity?

for eg, an object moved from stationary, speed up to 2m/s for 30min, then slower down to 1m/s and speed up to 5m/s for 1 hour, then finally it stop and remain stationary again. the work done in this case is also considered as zero?

if i apply a force on a stationary object, and it move a certain time after the force has removed. should i take the zero as initial velocity or the instantaneous velocity when the force just applied on it?