1. Work done is the energy transferred when a force moves an object over a distance. Since work is energy transferred, the unit for work is the joule (J). 20 N of friction 20 N of push

2. For example, work is done by the person when they push a block over a distance. 20 N of friction 20 N of push 10 kg 2 m

3. For example, no work is done by the person when they push a block and it doesn’t move. 30 N of friction 30 N of push 100 kg 0 m

4. Work is only done when the force moves the object. If the object doesn’t move, then no work has been done (as no energy has been transferred). 20 N of friction 20 N of push 10 kg 2 m

5. 20 N of friction 20 N of push 10 kg 2 m W = F x d = 20 N x 2 m = 40 Nm = 40 J It is assumed that no energy is lost to friction (thermal energy) when the energy transfers.