## September 13, 2011

### 4.9 Work

Recall and use the relationship between work, force and distance moved in the direction of the force:

$Work\: done\: =\: force\: \times \: distance\: moved$

Examples
1. A man pushes a 40N wheelbarrow 20m, how much work is he doing?
$Wd\: =\: F\: \times \: d$
$Wd\: =\: 40N\: \times \: 20m$
$Wd\: =\: 800j$

2. A skier skis 50m down a slope with 10N of friction acting against his motion, he descends 10m vertically down the slope. How much work has he done?

What measurement do we use as the distance? Well, we must remember to use the distance running in the same direction as the force acting against the object, so we use the length the skier travelled (50m) appose to his vertical height, so:

$Wd\: =\: 10N\: \times \: 50m$
$Wd\: =\: 500J$