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Collision question - Simple one

  • Thread starter nukeman
  • Start date
  • #1
655
0

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

 

Answers and Replies

  • #2
DaveC426913
Gold Member
18,643
2,115

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 = ?
 
  • #3
655
0
what the heck, I am still getting 3.9 :(

im going (65)(2.4)=(40)(x) solve for x, which = 3.9
 
  • #4
390
1
You should have a 2.9 instead of your 2.4 :)
 
  • #5
DaveC426913
Gold Member
18,643
2,115
You should have a 2.9 instead of your 2.4 :)
I imagine he's beating his head on his keyboard right about now...:tongue2:
 
  • #6
655
0
Haha, Dave, yes I was!

Thanks, I guess my 4's look way too much like 9's :)
 
  • #7
DaveC426913
Gold Member
18,643
2,115
Haha, Dave, yes I was!

Thanks, I guess my 4's look way too much like 9's :)
on ... your ... keyboard ? :bugeye:
 
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