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Circular Motion Help (1 Viewer)


Aug 2, 2005
Eastern Suburbs
this is from the 2003 HSC Paper Q4:

(a) A particle P of mass m moves with constant angular velocity ω on a circle of
radius r. Its position at time t is given by:
x = r cos θ
y = r sin θ,
where θ= ωt.
(i) Show that there is an inward radial force of magnitude mr ω2 acting on P.

i got as far as x''=-ω2x and y''=-ω2y

but then i got stuck after that and i checked solutions and in their answer they stated that the force is m[sqrt(x''2 + y''2)], i get the whole f=ma thing, but i dont understand why they had to use the right angle triangle in this and they didnt just sum the acceleration components like they do with force. i mean isnt acceleration just f/m and if m is constant then its essentially the same as f... why can we sum forces but not acceleration? :<

edit: okay disregard, its hot and my room is small and im tired and sweaty and wasn't thinking @_@, i forgot that they were in different planes and i was thinking complex number vectors and oh dear god i confused my self a hell of a lot :<
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