Energy is 'lost' or not used effectively when frictional forces occur. For example, when a bike applies its brakes and slows down the kinetic energy of the bike is transformed into heat energy in the brakes.
How much energy is lost depends on the frictional force (\(F\)) and the distance over which the frictional force is acting (\(d\)).
This is called the Work Done against Friction (\(E_{w}\)).
Work Done = frictional force x distance
\( E_{w}=F\times\,d\)
Example
Travelling between stops, the average frictional force on a bus was \(8\cdot2\times10^{3}N\) over a distance of 500\(m\).
Calculate the work done by the bus engine to overcome this frictional force.
