Impulse and momentum in two dimensions - Finding velocity

[Specter]

Homework Statement

In a physics lab, 0.30 kg puck A, moving at 5.0 m/s [W], undergoes a collision with a 0.40 kg puck B, which is initially at rest. Puck A moves at 4.2 m/s [W 30 N] . Find the final velocity of puck B.

Homework Equations

Conservation of momentum
Pythagorean theorum

The Attempt at a Solution

[/B]
I understand the steps I need to take to solve this question but once again I am getting a different answer than what I find online. Any help on where I went wrong would be great.

Let north and east be positive.

My diagram of the x and y components

https://i.imgur.com/0F5MsrP.png

Using conservation of momentum for the components

X-components:
(Not sure if all of the subscripts are correct in this part)
m₁v_1ox+m₂v_2ox=m₁v_2fx+m₂v_2fx
(0.30)(-5)+(0.40)(0)=(0.30)(-3.64)+(0.40)v_2fx
-1.5=-0.692
v_2fx=-0.808

The answer online for this was -1.0. Was it just rounded down or did I go wrong somewhere?

For the y-component:

m₁v_1oy+m₂v_2oy=m_2v1fy+m₂v_2fy
(0.30)(0)+(0.40)(0)=(0.30)(2.1)+(0.40)v_2fy
0=1.03
v_2fy=1.03

The answer online for this was -1.6, so I went wrong here too?

I didn't go beyond this part because I think my answers are wrong. I know that next I create a triangle with my answers and use pythagoreans theorem to solve for the missing side, then I use tan to find the direction and I have the final velocity with it's direction.

Also I haven't learned this yet but does the "o" in "v_1o" mean initial? Does the "f" in v_1f mean final?

 

[kuruman]

The method is correct. Recheck your calculations because it looks like you have made calculator errors.

"0" (zero not the letter o) as a subscript usually stands for "initial" as in time t = 0. With collision it makes more sense to use "i" and "f" for "initial" and "final".

 

[Specter]

The method is correct. Recheck your calculations because it looks like you have made calculator errors.

"0" (zero not the letter o) as a subscript usually stands for "initial" as in time t = 0. With collision it makes more sense to use "i" and "f" for "initial" and "final".

I double checked my calculations and I am still getting the same answers. I can't figure out where I have gone wrong.

 

[kuruman]

(0.30)(-5)+(0.40)(0)=(0.30)(-3.64)+(0.40)v2fx

This is correct.

-1.5=-0.692

This directly below the correct expression is nonsense and does not follow.

(0.30)(0)+(0.40)(0)=(0.30)(2.1)+(0.40)v2fy

This is correct.

0=1.03

This directly below the correct expression is nonsense and does not follow.

Since when is -1.5 is equal to -0.692 and 0 is equal to 1.03 anyway? Perhaps you need to improve your algebra skills.

 

[haruspex]

Please post the details of this step. I get a different result.

(0.30)(-5)+(0.40)(0)=(0.30)(-3.64)+(0.40)v2fx
v2fx=-0.808

 

[Specter]

This is correct.

This directly below the correct expression is nonsense and does not follow.

This is correct.

This directly below the correct expression is nonsense and does not follow.

Since when is -1.5 is equal to -0.692 and 0 is equal to 1.03 anyway? Perhaps you need to improve your algebra skills.

Wow that was a stupid mistake. Here's what I think are the correct answers.

m₁v_1ox+m₂v_2ox=m₁v_2fx+m₂v_2fx
(0.30)(-5)+(0.40)(0)=(0.30)(-3.64)+(0.40)v_2fx
-1.5+0=-1.092+0.40v_2fx
-0.408/0.40
v_2fx=1.02

m₁v_1oy+m₂v_2oy=m_2v1fy+m₂v_2fy
(0.30)(0)+(0.40)(0)=(0.30)(2.1)+(0.40)v_2fy
0=0.63+0.40v_2fy
-0.63=0.40v_2fy
v_fy2=-1.575

 

[Specter]

Please post the details of this step. I get a different result.

I think I figured it out in my latest reply.