nuvaj97

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How do I know that I have to convert this into seconds?  

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  How do I know when to use: UGf =UGi -Thermal energy.

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    How did they get 6.79*10^6m as the equation in this last picture here:

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How does when rubber slides on dry concrete, it experiences 5x more friction than when it slides on icy concrete in this picture:  

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how do I know when to use a=net force/change in time or when to use a=net force/mass in this picture: And here is the rest of the problem:

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Look at the top photo. How do I know where Net force "Fy" and Acceleration "Ay" is located on the free-body diagram?  

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I don't understand how final impulse = change in momentum - initial impulse when both initial and final impulse is (mi)vi or (mf)vf?    

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It says for the answer 25m/s is the final velocity. How is that so? And how do I know that the helmet's velocity is at 0m/s?

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How did they have "0" for M2V2?

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I don't understand how to do "Substituting using a=change in velocity /change in time." I know that it gave me the answer, but how do I get the answer? And same with "Substituting using P=m* change...