Question

a 45.0-kg woman stands up in a 60.0-kg canoe 5.0 m long. she walks from a point 1.00 m from one end to a point 1.00 m from the other end. if you ignore resistance to motion of the canoe in the water, how far does the canoe move during this process?

Answer 1

Measure the CM from the left end of the canoe

M x = (45 * 1 + 2.5 * 60) M = 105

x = (45 + 150) / 105 = 1.86 m from left end

After she walks 3 m the CM is from the left end

M y = (45 * 4 + 60 * 2.5)

y = (45 * 4 + 60 * 2.5) / 105 = 3.14 m

The left end of the canoe has moved 1.28 m to left

(The CM cannot move without an external force)

Check:

She increases the CM by 45 (3 - 1.28) = 77.4

Canoe movement decreases the CM by 60 * 1.28 = 76.8

1.28 is close