Conservation of momentum question

[David112234]

Homework Statement

Homework Equations

m1v1+m2v2=m1v1+m1v1 after

The Attempt at a Solution

my answer = -1m1v1
because the wall is not moving so its velocity is 0
therefore
m1v1 = m1-v1 after
I put -v because it is the same just bounces in the opposite X direction
I found somewhere online the answer should be 2 * mv * sin(θ)
I don't understand why

 

[haruspex]

because the wall is not moving so its velocity is 0
therefore
m1v1 = m1-v1 after

Conservation of momentum only applies to a closed system, i.e. no outside forces. The wall exerts a force. If you include the wall, the Earth exerts a force on the wall. If you include the Earth then in fact it will acquire a velocity from the impact, but so small you could not possibly measure it.
Just consider the change in momentum of the ball (as a vector).

 

[David112234]

Conservation of momentum only applies to a closed system, i.e. no outside forces. The wall exerts a force. If you include the wall, the Earth exerts a force on the wall. If you include the Earth then in fact it will acquire a velocity from the impact, but so small you could not possibly measure it.
Just consider the change in momentum of the ball (as a vector).

It is the same as before only its x component changes, first it goes right, then it goes left

 

[haruspex]

It is the same as before only its x component changes, first it goes right, then it goes left

The magnitude is the same as before, but momentum and velocity are vectors. What is the net change in velocity?

 

[David112234]

The magnitude is the same as before, but momentum and velocity are vectors. What is the net change in velocity?

Oh so I do vector addition
I did the math out and got the same answer, thank you