Ricardo mass 85 kg and Carmelita who is lighter are enjoying

Ricardo, mass 85 kg and Carmelita, who is lighter, are enjoying Lake Merced at dusk in a 30 kg canoe. When the canoe is at rest in the placid water, they exchange seats, which are 3.0 m apart and symmetrically located with respect to the center of the canoe. Ricardo notices that the canoe moved 37.1 cm relative to a submerged log during the exchange and calculates Carmelita\'s mass, which she has not told him. What is it?

Solution

x_com = m_R x_R + m_B x_B + m_C x_C / ( m_R +  m_B +  m_C)

-0.1855 = 85 * -1.5 + 0 + m_C (1.5 m) / ( 85+ 30+  m_C)

-0.1855 * ( 115+  m_C) = -127.5 + m_C (1.5 m)

127.5 - 21.33 = m_C (1.5 m + 0.1855)

m_C = 62.99 kg