# Homework Help: Changing places in canoe - find mass

1. Oct 17, 2007

### Dynex

Ricardo, of mass 82 kg, and Carmelita, who is lighter, are enjoying Lake Merced at dusk in a 38 kg canoe. When the canoe is at rest in the placid water, they exchange seats, which are 3.1 m apart and symmetrically located with respect to the canoe's center. Ricardo notices that the canoe moves 58.4 cm horizontally relative to a pier post during the exchange and calculates Carmelita's mass. What is it?

Thankz to any one who can show how to solve this really appriciate it.

2. Oct 17, 2007

### learningphysics

Think center of mass. There is no net force acting on the system of Ricardo+Carlita+boat... so the center of mass must remain motionless.

Call carlita's mass m.

Take a fixed axis from which you measure the position of the center of mass...

what is the initial position of the center of mass from this axis in terms of m?

what is the final position of the center of mass from this axis in terms of m (remember that the boat moves 58.4cm)?

initial position = final position...