When a coolie walks on a horizontal platform with a load on his head, the work done by the coolie on the load is zero.

Work is defined as the amount of energy transferred when an object moves due to an external force. Work is represented as the product of force and displacement. The SI unit of work is Joule (J). 
Energy is the capacity to do work. 
Power is the rate at which energy is transferred or transformed over time. Power has units of watts and can be calculated using the formula P=W/t, where W is work and t is time. 
The formula for power can also be simplified to P = Fv, where F is force and v is velocity.