Question

why does a labourer tie a piece of cloth on head while carrying heavy load??

Answer 1

Placing the load on the turban increases the area on which the load is placed i.e. the area of contact of the load increases. When the area on which pressure of the load is exerted increases, the pressure per unit area decreases. As a result, the pressure on their heads get readuced. This is why porters wear turbans while carrying heavy loads.
Hope this will be helpful :)

Answer 2

while carrying a heavy load on the head,the head will pains so to reduce the pain they will tie a piece of cloth on the head.