An 80 kg person decides to jump off the back end of a 30 kg canoe. His friend measures the speed of the canoe after he jumps to be 0.8 m/s. The canoe was initially at rest. What rule would I use to find the speed of the person who jumped?

Answer 1

initially there was 0 momentum. That momentum is conserved. So, assigning the canoe's direction as negative,

30*(-.8) + 80*v = 0
80v = 24
v = +.3m/s

Answer 2

conservation of momentum

initial mometum= final momentum
(80+30)Vc=30*.8-80*V

but Vc=0, the canoe was not moving initially. Solve for V