From my very limited knowledge of calculus I would have thought that if mass is assumed constant d/dt (1/2mv^2) = 1/2m2v. This seems to be corroborated by one website http://www.newton.dep.anl.gov/askasci/phy05/phy05008.htm and seems to follow the general rule d/dt (x^n) = nx^(n-1)(adsbygoogle = window.adsbygoogle || []).push({});

However in the Feynman lectures (Volume 1 13-1 (13.2)) http://student.fizika.org/~jsisko/K...Vol 1 Ch 13 - Work and Potential Energy 1.pdf he states that if mass is assumed constant d/dt (1/2mv^2) = 1/2m2v(dv/dt).

Could someone help explain what I have most likely misunderstood?

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# The derivative of Kinetic Energy

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