Question Regarding Velocity-Time Graphs

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The discussion revolves around analyzing a velocity-time graph of a train, with tasks to create position-time and acceleration-time graphs and calculate the train's acceleration at 3.0 seconds. The calculated acceleration is confirmed as 1 m/s², but the position-time graph is criticized for not being parabolic between 0 and 4 seconds. Additionally, there is a suggestion to verify the position at 2 seconds. Overall, while the acceleration calculation is accurate, the graphical representations require significant improvement.
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Homework Statement



The figure below shows the velocity-time graph of a train that starts from the origin at t = 0s

5d714o.jpg


a) Draw a position-time graph and an acceleration-time graph for the train

b) Find the acceleration of the train at t = 3.0 s

Homework Equations



a = Vf - Vi / t

x = 1/2 at^2 + Vi x t + Xi


The Attempt at a Solution



a)
xfq3w6.jpg


b) 1 m/s^2

Do my answers look right? If not, what did I do wrong?
 
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The acceleration is correct, and the graph of x(t) is almost correct, only the part between 0 and 4 s does not look parabolic, and check x at t=2 s. ehild
 
Looks right to me. But those are really, really, truly, bad graphs.
 
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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