Center of Mass problem: 40kg child on a boat catching a turtle

[saskiwi4]

Homework Statement

A 40 kg child stands at one end of a 70 kg boat that is 4 meters in length. The boat is initially 3 meters from the pier. The child notices a turtle on a rock near the far end of the boat and proceeds to walk to that end to catch the turtle. Neglect friction b/w the boat and water.

a. describe the subsequent motion of the sysyem (child+boat)

b. where is the child relative to the pier when he reaches far end of the boat?

c. Does he catch the turtle? (The child can reach out 1m in front of him.)

Homework Equations

The Attempt at a Solution

I can't figure out how to solve this at all. It is a practice problem for my test tomorrow and I simply do not understand how to do COM problems... All help is much appreciated!

 

[Panphobia]

That was a question on my physics assignment, either we're in the same class or this is a very common question. But anyway the centre of mass of the child+boat never changes so as the child walks forward the boat moves back so that the centre of mass stays the same.