# Elastic Collision - Ice Hockey

• papereater33
In summary: Welcome to PF papereater33!In summary, a hockey player skate at 7.85 m/s and has a mass of 120 kg when he collides with an another stationary hockey player. The second hockey player is now moving at 5.67 m/s. Find the mass of the second player and the speed of the first.
papereater33

## Homework Statement

A HOCKEYPLAYER SKATES AT 7.85 M/S AND HAS A MASS OF 120 KG WHEN HE COLLIDES WITH ANOTHER STAIONARY HOCKEY PLAYER. THE SECOND HOCKEY PLAYER IS NOW MOVING AT 5.67 M/S. FIND THE MASS OF THE SECOND HOCKEY PLAYER AND THE SPEED OF THE FIRST. ASSUME THIS COLLISION IS ELASTIC.

## Homework Equations

[Rho]playerone + [Rho]player2 == [Rho]playeroneafter + [Rho]player2after
^^^ COnservation of Momentum
And then Another Equation Which Escapes me.

## The Attempt at a Solution

Find: Pplayer1, Pplayer2,

How do I find the Mass and Speed?

I have been doing Collision Problems for some time now, but must have gotten hit too hard in hockey, because I am lost!

Many Thanks from Frigid CT

What does it mean when the collision is "elastic"?

AM

Welcome to PF papereater33!

You have two unknowns. One is the mass of the second player. The other unknown is the speed of player 1 after the collision.

Using conservation of momentum, you can relate these two unknowns to each other (i.e. solve for one in terms of the other). That leaves you with only one unknown. To solve for this unknown (and hence the other one), you need a second constraint on the system (i.e. a second equation). This constraint comes from the fact that the collision is elastic, which means that kinetic energy must also be conserved (total KE before = total KE after). Does that give you a hint as to what the second equation that escaped you is?

Oh, and by the way, it's typical to use the Roman letter p for momentum (not the Greek letter rho, which is usually used for density).

EDIT: Sorry if I messed up your attempt to guide the OP in the right direction Andrew Mason.

Wow, thanks guys for the prompt responses.

Okay so I need to use the conservation of Energy theorem?

1/2*M*V^2?

Eh?

Solve For Mass, and Plug that Back into the Conservation of Momentum?

Anyone Care To Elaborate? I am lost.

papereater33 said:
Anyone Care To Elaborate? I am lost.

What you described in post 4 is exactly what you need to do, so I'm not sure what you want us to elaborate on. Maybe post your attempt so far and tell us which part specifically is tripping you up?

"What does it mean when the collision is "elastic"?"

The collision is elastic because both momentum and energy is conserved at the point of the collision. In an inelastic collision, some momentum and evergy is lost. For an inelastic collision, think about a bullet hitting a wooden box, which in turn makes the box slide on the floor. the bullets' energy and momentum is lost inside of the block and they become "one complete object."

Thanks Guys!

I solved the problem for a Mass of 212 kg and a Velocity of 2.18 m/s? Is that Right?

papereater33 said:
Thanks Guys!

I solved the problem for a Mass of 212 kg and a Velocity of 2.18 m/s? Is that Right?

You should really post your solution if you want us to check it.

papereater33 said:
Thanks Guys!

I solved the problem for a Mass of 212 kg and a Velocity of 2.18 m/s? Is that Right?
That is a very heavy hockey player! What direction is the final velocity of the first player? The total momentum is too high if he is going in the same direction as his initial velocity.

AM

## 1. What is an elastic collision in ice hockey?

An elastic collision in ice hockey occurs when two objects, such as hockey players or the puck, collide and bounce off each other without any loss of kinetic energy. This means that the total energy before and after the collision remains the same.

## 2. How is momentum conserved in an elastic collision in ice hockey?

Momentum is conserved in an elastic collision in ice hockey because the total momentum of the system before the collision is equal to the total momentum after the collision. This means that the combined mass and velocity of the two objects remains constant.

## 3. What factors affect the elasticity of a collision in ice hockey?

The elasticity of a collision in ice hockey can be affected by factors such as the material and shape of the objects involved, the speed and angle of the collision, and the surface on which the collision occurs. These factors can influence how much kinetic energy is transferred during the collision.

## 4. How does the coefficient of restitution impact an elastic collision in ice hockey?

The coefficient of restitution, or the ratio of the velocity of separation to the velocity of approach during a collision, can impact the elasticity of a collision in ice hockey. A higher coefficient of restitution means a more elastic collision, while a lower coefficient of restitution means a less elastic collision.

## 5. Can an elastic collision occur in ice hockey even if there is friction present?

Yes, an elastic collision can still occur in ice hockey even if there is friction present. Friction may affect the speed and direction of the objects after the collision, but as long as the total kinetic energy is conserved, the collision can still be considered elastic.

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