# Velocity and Direction of a System after Inelastic Collision

• prockotyler
In summary: In any case, using conservation of momentum in two directions should not be a problem. The mass of the puck is given, but the mass of the player is not. However, it cancels out of the equations. Also, as @PeroK suggests, energy is not a good choice for this problem.In summary, the problem involves a 30.0-kg hockey player initially moving at 2.00-m/s to the right, catching a puck with a mass of .18 kg moving at 35.0-m/s at an angle of 60 degrees. The player and puck form a single object for a few seconds. The collision is determined to be inelastic because the kinetic energy after the collision
prockotyler

## Homework Statement

A hockey player with a mass of 30.0-kg is initially moving 2.00-m/s to the right. He catches on the stick a puck initially moving at 35.0-m/s at an angle of 60 degrees. The puck's mass is .18 kg and the player and puck form a single object for a few seconds. (A) Determine the direction angle and speed of the puck AND skater after the collision. (B) Was this collision elastic or inelastic? Prove it with numbers.
http://imgur.com/q8IDYQb
SORRY FOR THE TERRIBLE DRAWING... kind of in a hurry.

2. Homework Equations

Pbefore = Pafter >>> MV + mv = (M+m)V
Conservation of kinetic energy and 1/2mv2

## The Attempt at a Solution

(A): 1.89-m/s , 5.48 degrees
(B): inelastic because K < K0

I understand B, mostly. You just find the kinetic energies of the systems before and after and compare them. If they don't match up, it has lost some KE and you know it's inelastic. But, part A really messes me up. I tried just plugging in the numbers for my first relevant equation, then I realized I probably needed to find the components of each and then find the resultant ones. Any help would be amazing.
-TP

First, let me say this is a terrible problem. A hockey player is not an inert object that gets knocked around by a puck. He could stop a puck without moving if he wanted to. It's not that different from stopping a soccer ball without getting knocked backwards.

That said, if you imagine the player has no grip on the ice, you need to use momentum conservation in two directions for part A.

You cannot use energy because you do not know how much was lost, so you need another equation. You are told that the two form a single object for a while. What equation does that give you?
With regards to @PeroK's critique, I offer a slightly different view. A reasonable supposition is that a skater has negligible friction in the direction of travel, but will never slide orthogonally to that. On that basis, you could use conservation of momentum in the skater's original direction, but assume the skater's direction does not change. Whether that is what the question intends I cannot tell.

## 1. What is the definition of velocity in physics?

Velocity is a measure of the rate at which an object changes its position in a specific direction. It is a vector quantity, meaning it has both magnitude (speed) and direction.

## 2. What is an inelastic collision?

An inelastic collision is a type of collision in which the total kinetic energy of the system is not conserved. This means that some of the kinetic energy is converted into other forms of energy, such as heat or sound.

## 3. How is the velocity of a system calculated after an inelastic collision?

The velocity of a system after an inelastic collision can be calculated using the conservation of momentum principle. This states that the total momentum of the system before the collision is equal to the total momentum after the collision. The equation for this is: m1v1 + m2v2 = (m1 + m2)v, where m1 and m2 are the masses of the objects and v1 and v2 are their velocities before the collision, and v is the velocity of the system after the collision.

## 4. How does the direction of a system change after an inelastic collision?

The direction of a system after an inelastic collision will depend on the direction and velocity of the objects involved in the collision. If the objects are moving in the same direction, the direction of the system will remain the same. However, if the objects are moving in opposite directions, the direction of the system will change to reflect the combined momentum of the objects.

## 5. What factors can affect the velocity and direction of a system after an inelastic collision?

The velocity and direction of a system after an inelastic collision can be affected by the masses, velocities, and angles of the objects involved in the collision. Other factors such as external forces and friction can also play a role in determining the final velocity and direction of the system.

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