- #1

ilovedeathcab

- 11

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**calculating final speed using momentum [solved]**

1. A 73.8 kg girl runs at 4 m/s and jumps onto a 3.4 kg stationary skateboard. Ignore friction and calculate the final speed of the girl.

* DO NOT include units in your answer.

* Give your answer with one decimal.

* Answers will be accepted if they are within 0.2 of the correct answer.

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2. I understood that this uses the law of conservation of momentum, but couldn't get past this basic equation without getting it wrong.

m1v1i + m2v2i = m1v1f + m2v2f

Assuming object 1 is the girl, and object 2 is the skateboard, v2i would equal 0 (stationary skateboard), v1i would equal 4m/s (girl), and you would plug in the masses (m1=73.8, m2=3.4kg). I'm not sure what to put in for v2f, becuse it doesn't specify in the problem the final velocity of the skateboard. I'm pretty sure I'm missing the big picture.

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