- #1

Balti

- 6

- 1

- Homework Statement
- Dave and Paula are outside, playing upon frictionless ice provided by their physics teacher. Paula is stationary when Dave, sliding with velocity v suddenly crashes into her. They move off together. Dave has twice the mass of Paula. What percentage of the initial kinetic energy remains after the collision? Give your answer to two significant figures.

- Relevant Equations
- ##E_k=\frac 1 2 (m)(v^2)##

I suppose

Firstly I tried defining into an equation to make the whole thing more 'tangible'.

##m_1= Paula's~Weight⋅2 = m_p⋅2##

##m_2= \frac {Dave's~weight}{2} = \frac {m_d}{2}##

##E_k1= \frac 1 2 (m_p⋅2)(0^2)##

##E_k1= \frac 1 2 (2m_p)##

##E_k1= m_p ##

##E_k2= \frac 1 2 (\frac {m_d} {2}) (v^2)##

##E_k2= ({m_d}) (v^2)##

And I guess

##E_k2=({m_d}) (v^2) ({m_p})##

And as I'm told we find the change of kinetic energy by

##ΔE_k={E_k2}-{E_k1}##

And then I get stuck. Provided, it is 2 am and I am dead exhausted.I don't want an answer, I just want a direction to go in. I was never really good with having a few variables and you figure it out with formula manipulation. I don't know, just not really my thing.

Any help?

##m_1= Paula's~Weight⋅2 = m_p⋅2##

##m_2= \frac {Dave's~weight}{2} = \frac {m_d}{2}##

**Before impact**##E_k1= \frac 1 2 (m_p⋅2)(0^2)##

##E_k1= \frac 1 2 (2m_p)##

##E_k1= m_p ##

**After Impact**##E_k2= \frac 1 2 (\frac {m_d} {2}) (v^2)##

##E_k2= ({m_d}) (v^2)##

And I guess

##E_k2=({m_d}) (v^2) ({m_p})##

And as I'm told we find the change of kinetic energy by

##ΔE_k={E_k2}-{E_k1}##

And then I get stuck. Provided, it is 2 am and I am dead exhausted.I don't want an answer, I just want a direction to go in. I was never really good with having a few variables and you figure it out with formula manipulation. I don't know, just not really my thing.

Any help?

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