Man on a Boat: Finding the Center of Mass

[aszymans]

Homework Statement

A man with mass m1 = 60 kg stands at the left end of a uniform boat with mass m2 = 165 kg and a length L = 3.6 m. Let the origin of our coordinate system be the man’s original location as shown in the drawing. Assume there is no friction or drag between the boat and water.

Homework Equations

If the man now walks to the right edge of the boat, what is the location of the center of mass of the system

The Attempt at a Solution

I tired using the equation xcom = m1x1+m2x2 / Mtotal
60*3.6 + (1.8)(165)/(165+60) which = 2.28 which is wrong

 

[grzz]

Why don't you use moments about the centre of mass rather than plugging in numbers in a formula?

 

[gneill]

Homework Statement

A man with mass m1 = 60 kg stands at the left end of a uniform boat with mass m2 = 165 kg and a length L = 3.6 m. Let the origin of our coordinate system be the man’s original location as shown in the drawing. Assume there is no friction or drag between the boat and water.

<snip>

I tired using the equation xcom = m1x1+m2x2 / Mtotal
60*3.6 + (1.8)(165)/(165+60) which = 2.28 which is wrong

First determine the location of the C.O.M. before the man moves. Remember, the coordinate system is fixed to the man's original location in space, not to the man himself.

Next, consider whether the system comprising the man and boat is open or closed with respect to forces; are there only internal forces acting, or are there external forces acting on the system components? What do you know about the behavior of the center of mass of a closed (or isolated) system?