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How fast are the two moving if she has a mass of 45kg?

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a raft in a lake is initially moving towards the shore with a speed of 1.0m/s. Sally runs to the water and jumps onto the raft with a speed of 4.0m/s

asked Dec 16, 2013 in Highschool Physics by anonymous

1 Answer

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This is a problem about momentum conservation. When she lands on the boat, the two are having an inelastic collision. Using momentum conservation, find the initial and final momentum and make them equal.

First set up a coordinate system, make the boat traveling to the left initially and make Sally run to the right initially. Set right to be the positive x direct. $$P_i=45kg\times 4.0m/s-m_{boat}\times (1.0)m/s=(45kg+m_{boat})\times v_f$$

||v_f|| is the velocity of the two moving together after Sally jumps on the boat. The issue is that we don't know the boat's mass -- is it given in the question?
answered Dec 17, 2013 by PhysicsDude (21,750 points)
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