(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A 2100kg van collides with a 1200kg car that is at rest. They lock together and move together at a speed of 4.5 m/s. What is the initial speed of the van?

2. Relevant equations

Eki = Ekf

1/2mv^2

3. The attempt at a solution

Okay, so I know that the energy before the collision must equal the energy after the collision. I know everything I need to figure out the energy after the collision:

E = 1/2mv^2

(1/2)(2100kg + 1200kg)(4.5m/s)^2

=33412.5 J

So now I need to figure out the other side of the equation using that number. So:

33412.5 = 1/2mv^2

v^2 = 2(33412.5J)/m

=2(33412.5J)/2100kg

Square Root of the result gives me:

5.6 m/s

That looks right to me, but my worksheet says the answer should be 7.07 m/s. What am I doing wrong?

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# Momentum Collision

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