slight differentiation problem (1 Viewer)

[fashionista]

i was doing a worked circular motion question and this is where i got stuck

x=ra-rsin(a)

therefore x dot= r(a dot-a dot cos(a))

ok so i cant type theta in so i made theta= a
and the velocity is x with a little dot on top so i made it =x dot
and angular velocity equals theta with a little dot on top so i made it = a dot

in the equation for x dot, where does the a dot in front of cos(a) come from???
when u differentiate sin(a) shouldnt it just equal cos(a)???

 

[funk_master81]

try x dot(a)

 

[fashionista]

how do u mean? ( im sorry if i sound really dumb but for some reason its not clicking)

OH my gosh *SMACKS HEAD* i understand!! sorry for troubling u with a stupid stupid obvious question

 

[fashionista]

oh i also have another question,
a point is moving in a circle. Prove that it's angular velocity about the centre is twice it's angular velocity about any fixed point on the circumference.

i dont think im made for circular motion

 

[CrashOveride]

remember circle geo, angle at centre twice that of angle at cirum standing on same arc

 

[funk_master81]

no worries love, im here to help

 

[fashionista]

man u guys are great, thanks a bazillion

 

[funk_master81]

any more 'brain busters'?

 

[Slidey]

Sure. Prove a polynomial is complete in non-polynomial time.

 

[Jase]

Well, let x=Polynomial and y=NP. Now consider the graph y=x.
Clearly, by inspection, y=x.

Hence P=NP. Now where's my million dollars.

 

[funk_master81]

thanks Jase but he/she did ask me.

you're right though