By wearing the helmet, the time isextended during which the change in momentum of the body takes place during the crash.
This increase in time for the force acting on the body will decrease the impact of force on the body.
In the given graph, the value of force on the head is less and time taken is more in the first graph.
Thus, the first graph (1) represent the wearing helmet case.
The force on the head is more and time is less in the second case.
Thus, the second graph (2) represents the without helmet case.
