Momentum of colliding billard balls

The correct value for Vw is 3.92. In summary, two billiard balls with equal masses collide elastically with one initially at rest and the other moving at a velocity of 3.29 m/s. After the collision, the white ball moves at an angle of 21° above the horizontal while the black ball moves at an angle of 69° below the horizontal. The final speeds of the balls can be found using conservation of momentum. The calculation was attempted and an incorrect value of 3.66 was obtained for the white ball's final speed, which was due to a small error in the initial velocity. The correct value is 3.92 m/s.
  • #1
ElevatorNinja
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Homework Statement



A white billiard ball with mass mw = 1.43 kg is moving directly to the right with a speed of v = 3.29 m/s and collides elastically with a black billiard ball with the same mass mb = 1.43 kg that is initially at rest. The two collide elastically and the white ball ends up moving at an angle above the horizontal of θw = 21° and the black ball ends up moving at an angle below the horizontal of θb = 69°.
http://smartphysics.com/images/content/mechanics/ch12/billiardballsnew2.png

I need to find the final speeds of the balls.


Homework Equations



Conservation of momentum

The Attempt at a Solution




What I tried already was having initial momentum equal to final momentum. And then splitting it into x and y components and solving for the unknown velocities and got 1.4 for the black one and 3.66 for the white one. I'm not sure where I went wrong. Please help.

Here is some of my work:
Since masses cancel out, I have
for X: 3.92 + 0 = Vwcos21 + Vbcos69
for y: 0 = Vwsin21 - Vbsin69
Then solved for Vb, which I got 1.4, but it's wrong.
 
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  • #2
Your method is fine. You just swapped two digits in the initial velocity.
 

Related to Momentum of colliding billard balls

What is momentum?

Momentum is a measure of an object's motion and is calculated by multiplying its mass by its velocity. It is a vector quantity, meaning it has both magnitude and direction.

Why is momentum important in collisions?

Momentum is important in collisions because it helps us understand how objects behave when they collide. In a collision, the total momentum of the system is conserved, meaning it stays the same before and after the collision.

How does the momentum of colliding billiard balls change?

When two billiard balls collide, the total momentum of the system stays the same. This means that the momentum of one ball may change, but the other ball's momentum will change in the opposite direction so that the total momentum remains constant.

What factors affect the momentum of colliding billiard balls?

The momentum of colliding billiard balls depends on the mass and velocity of each ball. The heavier the ball and the faster it is moving, the greater its momentum will be. The angle and speed of the collision can also affect the momentum.

How is momentum useful in predicting the outcome of a collision?

By understanding the principles of momentum, we can predict the outcome of collisions between billiard balls or any other objects. By calculating the momentum of each object before and after the collision, we can determine the direction and speed of their movement after the collision.

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