Is Acceleration Zero When Velocity Is Zero?

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An object can have zero velocity while still experiencing non-zero acceleration, as it may be transitioning from negative to positive velocity. The displacement of a book moved around a table and returned to its starting point is zero, as displacement measures the change in position. Additionally, an object can have positive acceleration while slowing down if its velocity is negative, indicating that the acceleration and velocity are in opposite directions. These concepts highlight the distinction between velocity and acceleration in physics. The explanations provided are clear and accurate.
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Homework Statement



1. If an object has zero velocity, is its acceleration necessarily zero at that instant?

2. A book is moved around the perimeter of a table that is 1m x 2m. If the book ends up at its initial position, what is its displacement?

3. Can the sign of acceleration be positive for an object slowing down?

The Attempt at a Solution



1. No. Aan object could be accelerating from a negative velocity through a point of zero velocity. Therefore its acceleration is not zero, because it is speeding up.

2. Displacement is change in position, so the book's displacement is zero.

3. Yes, the sign of acceleration can be positive for an object that is slowing down. When an objects velocity and acceleration are in opposite directions, its speed decreases with time. An object with a negative velocity will slow down with a positive acceleration.

Are my explanations complete?

Thanks for any help!
 
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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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