Collision question - Simple one

[nukeman]

Homework Statement

Something I am doing wrong?

"A 65kg boy and his 40kg sister both wearing roller blades, face each other at rest. The girl pushes the boy hard, sending him backwards with a velocity of 2.90 m/s toward the west. Ignore friction.

What speed does the girl go?"

I cam up with m1(v1i - v1f) = m2(v2f - v2i)

Solved for v2f and got 3.9 m/s

But the correct answer is 4.71 m/s

?? Any help?

Homework Equations

The Attempt at a Solution

 

[DaveC426913]

Homework Statement

Something I am doing wrong?

"A 65kg boy and his 40kg sister both wearing roller blades, face each other at rest. The girl pushes the boy hard, sending him backwards with a velocity of 2.90 m/s toward the west. Ignore friction.

What speed does the girl go?"

I cam up with m1(v1i - v1f) = m2(v2f - v2i)

Solved for v2f and got 3.9 m/s

But the correct answer is 4.71 m/s

?? Any help?

Homework Equations

The Attempt at a Solution

m₁ * v₁ = m₂ * v₂
where
m₁ = 65
v₁ = 2.9
m₂ = 40
v₂ = ?

 

[nukeman]

what the heck, I am still getting 3.9 :(

im going (65)(2.4)=(40)(x) solve for x, which = 3.9

 

[JHamm]

You should have a 2.9 instead of your 2.4 :)

 

[DaveC426913]

You should have a 2.9 instead of your 2.4 :)

I imagine he's beating his head on his keyboard right about now...

 

[nukeman]

Haha, Dave, yes I was!

Thanks, I guess my 4's look way too much like 9's :)

 

[DaveC426913]

Haha, Dave, yes I was!

Thanks, I guess my 4's look way too much like 9's :)

on ... your ... keyboard ?