# Homework Help: Center of Mass boat distance from shore what am I doing wrong?

1. Mar 16, 2012

### sweetpete28

Problem: A symmetrical rowboat, mass M = 116 kg, length L = 6.89 m, points toward the shore. A man, mass m = 90 kg, stands in the back of the boat, distance d = 35.7 m from the shore. If the man now walks to the front of the boat, how far will he be from the shore?

Here is what I did:

Selected 0 as origin at shoreline:

Center of mass when man is in back of boat = [(90)(6.89) + (116)(3.445)] / (90 + 116) = 4.95 meters

When man is in front of boat he is distance d from shore and boat is distance d + 3.445:
Center of mass = [90d + 116(d + 3.445)] / (90 + 116) = 4.95
d = 3.01; so when man moves from back to front displacement is 3.01 m

So distance from shore is 35.7 + 3.01 = 38.7 m. But this answer is wrong. So what am I doing wrong???

2. Relevant equations

3. The attempt at a solution

2. Mar 16, 2012

### PeterO

The man was walking towards the shore, not away from the shore, so he will be closer that 35.7, not further.