Angular Momentum

I need some clarification on a homework problem related to angular momentum. I understand how to calculate the angular momentum by using L= IW but when calculating the moment of intertia for the particle i dont understand why to use .5m as the radius instead of .4m due to being placed at the 100 cm mark. From all the answers ive seen online and in the back of the book, the answer is calculated using .5m as the radius.

1. Homework Statement

A particle of mass 0.400 kg is attached to the 100-cm
mark of a meterstick of mass 0.100 kg. The meterstick
rotates on the surface of a frictionless, horizontal
table with an angular speed of 4.00 rad/s. Calculate
the angular momentum of the system when the stick

(a) perpendicular to the table
through the 50.0-cm mark and

(b) perpendicular to
the table through the 0-cm mark.

ehild
Homework Helper
I need some clarification on a homework problem related to angular momentum. I understand how to calculate the angular momentum by using L= IW but when calculating the moment of intertia for the particle i dont understand why to use .5m as the radius instead of .4m due to being placed at the 100 cm mark. From all the answers ive seen online and in the back of the book, the answer is calculated using .5m as the radius.

1. Homework Statement

A particle of mass 0.400 kg is attached to the 100-cm
mark of a meterstick of mass 0.100 kg. The meterstick
rotates on the surface of a frictionless, horizontal
table with an angular speed of 4.00 rad/s. Calculate
the angular momentum of the system when the stick

(a) perpendicular to the table
through the 50.0-cm mark and

(b) perpendicular to
the table through the 0-cm mark.

Where comes 0.4 m as radius come from? The meter stick is 100 cm long, and rotates about the axis going through its middle.