Question

A boy of mass 50kg is standing at one end of a boat of length 9m and mass 400kg. He runs to the other end.Find out the distance of the centre of mass of the boat -boy system through which it moves .

Answer 1

According to the question there is a boy of mass 50kg standing at the end point of a boat. Now, the boy starts to run to the other end,all the force applied inside the system. There is no force applied to outside of the system.

Complete Solution: Here we don’t apply any external force to the boat
So, the boat is not subjected to any external force.
The only force applied in this whole function is the frictional force with the boy and the surface of the boat
So, we can say the center of mass position will not change, there is zero change of the mass of the center.
Since there is no external force acting on the boat-boy system. And the center of mass was initially at rest.
So,it will remain at rest

Hence, distance through which center of mass= 0m

Note: The question is so easy but you must know that the whole system is the boy and boat,In this type of question the body moves internally the system then the center of mass never changes. Friction is a force that holds back the movement of a sliding object. That's it. You will find friction everywhere that objects come into contact with each other. The force acts in the opposite direction to the way an object wants to slide.