A 45 kg boy stands on a 180 kg boat at rest on calm water.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A boy stands on a boat at rest on calm water. He jumps off the front at . Ignore the water's drag.
- What is the total momentum before the jump?
- What is the boat's velocity just after?
Need a reminder? The key ideaShow
With no outside force, the total momentum of a group of objects stays the same: . Give opposite directions opposite signs. Things that start at rest end with equal and opposite momenta.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) Both at rest: .
Step 2. (b) , so , backwards.
Answer: ; backwards.
Check. : equal and opposite.
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