- #36

Frigus

- 337

- 157

According to this derivation of work done which makes sense to me and which is as follow,Not at all. $$\vec F \cdot \vec v = 0 \ \Rightarrow \frac{dK}{dt} = 0 \ \Rightarrow \frac{dv}{dt} = 0$$

PS Note that in post #11 I showed that: $$\frac{dK}{dt} = \vec F \cdot \vec v$$

v

_{x}

^{2}-u

_{x}

^{2}=2a

_{x}s---(I)

F

_{x}=Ma

_{x}---(II)

And after some little algebra we get,

##\frac{1}{2}\ ##mv

^{2}

_{x}-##\frac{1}{2} \ m##u

^{2}

_{x}=F

_{x}.s

It means to me that if their is change in speed of object due to the force then it has done work as their is change in kinetic energy of object and if force doesn't changes the kinetic energy then their is no work done which is case of perpendicular force as it doesn't changes the speed but only direction. I know you have shown that as f and v are perpendicular then their dot product is zero but I can't make physical sense from the dot product and I try to understand it physically.