What Is the Speed of the Second Puck After a Head-On Collision?

[lilmissbossy]

Homework Statement

ice hockey puck moving at speed V1 collides head on with a second identical puck moving towards it at speed V2. After the collision, the first puck slows down to speed v1 without changing direction.
a)After the collision what is the speed v2 of the second puck?
b) calculate the speed v2 of the second puck when the first puck had an initial speed of 18ms-1 that was changed to 2.0ms-1 by the collision, and the initial speed of the second puck was 12,0ms-1. both pucks have a mass of 0.16kg

The Attempt at a Solution

well the questions shows that the initial puck continues on its path at a lower speed to i guess this was an elastic collision

not sure if the math is right tho

m1V1+m2V2 = m1v1+m2v2
v2 = m1V1+m2V2/m1v1 + m2

when i factor in the given speeds and masses in the next part of the question i am not sure if it is right.

v2 = (0.16kg)(18.oms-1)+(0.16kg)(12.0ms-1)/(0.16kg)(2.0ms-1)+0.16kg
v2 = 15.16ms-1

is this right?

 

[tiny-tim]

Welcome to PF!

Hi lilmissbossy! I forgot to say earlier … Welcome to PF!

m1V1+m2V2 = m1v1+m2v2
v2 = m1V1+m2V2/m1v1 + m2

Nooo … v2 = (m1V1+m2V2 - m1v1)/m2.

Try again!

 

[LowlyPion]

Homework Statement

ice hockey puck moving at speed V1 collides head on with a second identical puck moving towards it at speed V2. After the collision, the first puck slows down to speed v1 without changing direction.
a)After the collision what is the speed v2 of the second puck?
b) calculate the speed v2 of the second puck when the first puck had an initial speed of 18ms-1 that was changed to 2.0ms-1 by the collision, and the initial speed of the second puck was 12,0ms-1. both pucks have a mass of 0.16kg

The Attempt at a Solution

well the questions shows that the initial puck continues on its path at a lower speed to i guess this was an elastic collision

not sure if the math is right tho

m1V1+m2V2 = m1v1+m2v2
v2 = m1V1+m2V2/m1v1 + m2

when i factor in the given speeds and masses in the next part of the question i am not sure if it is right.

v2 = (0.16kg)(18.oms-1)+(0.16kg)(12.0ms-1)/(0.16kg)(2.0ms-1)+0.16kg
v2 = 15.16ms-1

is this right?

The hockey pucks are identical. You can drop the mass out the equations. Might make it simpler.

 

[lilmissbossy]

Hi lilmissbossy! I forgot to say earlier … Welcome to PF!


Nooo … v2 = (m1V1+m2V2 - m1v1)/m2.

Try again!

Oh ok i see now i have made a mistake when rearranging the equation...
thats great i will factor in the values and it should make more sense

 

[ashvuck101]

so the answer is 28 m/s that doesn't make much sence?

 

[dgmatthews]

Hey guys, had the same problem.
Remember V is a vector quantity so if the pucks are heading toward each other one will be a negative quantity.

eg: (.16x18)+(.16x-12)=(.16x2)+(.16xV2)

so the answer is 4 not 28

Momentum Conservation
.96=.96