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How do I figure out the initial velocity of an object? 
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#1
Jul1410, 10:01 AM

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1. The problem statement, all variables and given/known data
Hi, I need to figure out the initial velocity if an object of 1400 kilograms is subjected to a friction coefficient (sliding friction) of 0.4587 for 75.6 metres, and its final velocity after being subjected to that friction is 23.05 metres per second. How do I go about this? 2. Relevant equations The only equations that I can think of that are relevant is: Fr=μmg distance=ut+0.5at^{2} Ek=0.5mv 3. The attempt at a solution Friction force= Fr=μmg Fr=0.4587*1400*9.8=6293.364 Final momentum p=mv p=32270N Final Kinetic energy Ek=0.5mv Ek=0.5*1400*23.05=16135J I'm not sure how to do the distance equation as I don't know the amount of time. 


#2
Jul1410, 10:07 AM

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P: 41,326

Two ways to go:
(1) Use kinematics. Use Newton's 2nd law to find the acceleration and combine that with some kinematic equations. (Look for a kinematic relationship that includes distance and velocity.) (2) Use energy. What's the work done by that friction force? FYI: KE = ½mv², not ½mv. 


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