Check My Work: 100kg Mass Moving in a Straight Line

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A 100 kg mass is influenced by a force F(t) = (120 N/s)t + 4000 N, and its speed at t = 5 s is being calculated. The initial calculation yields a force of 4600 N at t = 5 s, leading to a speed of 230 m/s using the formula V = (FΔT)/M. However, there is a discussion about whether to use the maximum force during the interval or the average force for a more accurate result. The importance of balancing change symbols in equations is emphasized, suggesting that using average force could provide a better understanding of the mass's motion. The conversation highlights the need for careful consideration in applying physics principles to ensure accurate calculations.
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I was wondering if someone could check my work and see if its correct.

An object of mass 100.00kg moves in a straight line under the influence of a force given by F(t)=(120 N/s)t+4000N
At t=0 it is moving at 0 m/s. Determine its speed at t=5.00 s

What i did is this. I plugged 5s into the function and got 4600N. Then i used F▲V=M▲V arranged to V=(F▲T)/M
V=(4600N X 5.00s)/100.0kg
V=230. M/S

Thank you
 
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\int_{0}^{5} (120t + 4000)dt = m \int_{0}^{v} dv
 
I hope that you meant F ▲t = m ▲v ... which DOES lead to ▲V = (F▲t)/m .
. . . ("change" symbols in an equation should ALWAYS balance) . . .

But why would you use the strongest Force in the 5-second duration?
Why not use the weakest Force, instead? . . . why not use the AVERAGE ?
. . . (ALWAYS multiply one's full range by the other's average) . . .
 
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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