Net External Force & Work Done: Explained & Justified

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A sailboat moving at a constant velocity experiences no net external force doing work on it, as work requires a change in energy or motion. When a particle's speed doubles, the net external force does more work during the second doubling due to the increased distance over which the force acts and the greater kinetic energy change involved. The discussion emphasizes the importance of demonstrating understanding before seeking help on homework questions. Participants are reminded to post homework queries in designated forums to ensure proper guidance. Understanding these concepts is crucial for grasping the relationship between force, work, and motion.
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A sailboat is moving at a constant velocity. Is work being done by a net external force acting on the boat? Explain.

The speed of a particle doubles and then doubles again because a net external force acts on it. Does the net force do more work during the first or the second doubling? Justify your answer.
 
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Welcome to PF Clark and Larry!

This seems like a homework question, so according to the forum rules, you must show your own thoughts on the problems before anyone can help you.

Also, please post future homework problems in the appropriate Homework forums:

https://www.physicsforums.com/forumdisplay.php?f=152
 

Thread 'Magnitude of buoyant force in fluids of different densities'

The book claims the answer is that all the magnitudes are the same because "the gravitational force on the penguin is the same". I'm having trouble understanding this. I thought the buoyant force was equal to the weight of the fluid displaced. Weight depends on mass which depends on density. Therefore, due to the differing densities the buoyant force will be different in each case? Is this incorrect?
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