If $\"\"$ is work in joules, $\"\"$ is force in newtons $\"\"$ is displacement of the object in meters.

$\"\"$ describes the work of the person and $\"\"$ describes the work done by the friction.

(a)

$\"\"$

$\"\"$ .

(b) When a person pushes a box $\"\"$ meters with a force of $\"\"$ newtons and friction exerts a force of $\"\"$ newtons.

Substitute $\"\"$ in $\"\"$ .

$\"\"$

$\"\"$ .

The network expended is $\"\"$ newtons per meter.

(a) $\"\"$

(b) The network expended is $\"\"$ newtons per meter.