Elastic and inelastic collisions

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In an inelastic collision within a closed system, momentum is conserved while total kinetic energy is not, leading to confusion about how changes in kinetic energy affect momentum. The key distinction is that kinetic energy is a scalar quantity, whereas momentum is a vector quantity, which allows for differing conservation laws. An example illustrates this: two equal masses moving toward each other at equal speeds collide, stick together, and come to rest, resulting in a total kinetic energy change while momentum remains conserved. Understanding these principles clarifies the relationship between kinetic energy and momentum in inelastic collisions. The discussion emphasizes the importance of recognizing the different properties of these two physical quantities.
MBBphys
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Homework Statement


In a closed system, in an inelastic collision, momentum and total energy is conserved, but total kinetic energy is not.
But how is this possible? If we have a change in total kinetic energy, we have a change in velocity, and so we must have a change in momentum as:
momentum=mass*velocity
So I am really confused!
Thanks :)

Homework Equations


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The Attempt at a Solution


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Keep in mind that kinetic energy is a scalar quantity and momentum is a vector quantity.

Think about the example of two equal masses moving toward each other with equal speeds and the two masses stick together and come to rest after they collide.
 
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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