Finding the Post-Collision Velocity: Is My Calculation Correct?

[Mowgli]

Homework Statement

Daisy (65.0kg) skates on ice at 4.5m/s to greet her friend (75.0kg), who is standing still, with open arms. As they collide, while holding each other, with what speed do the both move off together?

Homework Equations

MaVa+MbVb / Ma+Mb

The Attempt at a Solution

Is this correct?

(Va+b)=75(0)+(65)(4.5) / 75+65
= 0+69.5 / 140
= .496m/s

 

[mizzy]

using the equation

m1v1 + m2v2 = (m1 + m2)vf

I think you forgot to multiply the speed of Daisy to her mass.

 

[bp_psy]

The Attempt at a Solution

Is this correct?

(Va+b)=75(0)+(65)(4.5) / 75+65
= 0+69.5 / 140
= .496m/s

(65)(4.5)=/=69.5
Multiplication not addition.

 

[Doc Al]

Homework Equations

MaVa+MbVb / Ma+Mb

Careful with parentheses. This should be: (MaVa+MbVb) / (Ma+Mb)

Redo your calculation.

 

[Mowgli]

So I got (75(0) + 65(4.5)) / (75+65)
= 0+292.5 / 140
= 2.1 m/s

 

[mizzy]

that's correct

 

[Mowgli]

thank you so much!