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EDIT: MASS OF CANOE IS ACTUALLY 50G I typed it wrong the 1st time :/

50kg girl sits in a 50kg canoe at rest on the water. She holds two 10 kg cannon balls. she throws them over the stern of her canoe one at a time, each ball leaving her hands at a velocity of 5.0m/s relative to the canoe. what is the final velocity of the canoe, neglecting friction between boat&water?

ΣP = ΣP'

P = MV

I don't really understand, probably misunderstood key concepts but I tried anyway.

1) finding momentum of 1st ball...

P = 5.0m/s * 10kg

=50 N*s

2) speed of boat after that 1st ball...

V = P/m

=50 N*S / (50kg + 50kg + 10kg)

=0.45m/s

3) here it gets tricky i think, and where I am lost. Because the speed is relative to canoe the speed of the 2nd ball should be

V= 5.0 m/s + 0.45 m/s = 5.45m/s ??

therefore

momentum of 2nd ball = 5.45m/s * 10kg = 54.5 N.s

and for the canoe's final velocity..

V = P/m

= 54.5 N.s / (50kg + 50kg)

= 0.54 m/smy answer books gives me 0.87 m/s and I am lost, so help pleeease ;D

## Homework Statement

50kg girl sits in a 50kg canoe at rest on the water. She holds two 10 kg cannon balls. she throws them over the stern of her canoe one at a time, each ball leaving her hands at a velocity of 5.0m/s relative to the canoe. what is the final velocity of the canoe, neglecting friction between boat&water?

## Homework Equations

ΣP = ΣP'

P = MV

## The Attempt at a Solution

I don't really understand, probably misunderstood key concepts but I tried anyway.

1) finding momentum of 1st ball...

P = 5.0m/s * 10kg

=50 N*s

2) speed of boat after that 1st ball...

V = P/m

=50 N*S / (50kg + 50kg + 10kg)

=0.45m/s

3) here it gets tricky i think, and where I am lost. Because the speed is relative to canoe the speed of the 2nd ball should be

V= 5.0 m/s + 0.45 m/s = 5.45m/s ??

therefore

momentum of 2nd ball = 5.45m/s * 10kg = 54.5 N.s

and for the canoe's final velocity..

V = P/m

= 54.5 N.s / (50kg + 50kg)

= 0.54 m/smy answer books gives me 0.87 m/s and I am lost, so help pleeease ;D

## Homework Statement

## Homework Equations

## The Attempt at a Solution

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