
#1
Aug1605, 09:45 AM

P: 51

i have been set the following question
theta = 3r^2 find the magnitude of the acceleration when r=0.8 m dr/dt = 4ms^1 d^2r/dt^2 = 12 ms^2 my working followed the process of calculating angular velocity with these conditions and angular acceleration with these conditions then plugging them into the acceleration formula for a polar coordinate system. when doing this i get a(radial) = 282.912 ms^2 (componant along the radius) a(theta) = 218.88 ms^2 (componant perpendicular to radius) using pythagoras to calculate the magnitude of the resultant acceleration i get a value 357.7 ms^2 a value my dynamics lecturer is prompt to tell me is WRONG. perhaps someone can help me...PLEASE 



#2
Aug1705, 09:44 AM

Sci Advisor
HW Helper
P: 1,937

Your numbers are wrong. I don't see how you could get them.
The radial acceleration is GIVEN to you as 12 m/s^2. You have to relate d^2theta/dt^2 to d2r/dt^2 by differentiating the equation theta=3r^2 twice. Then rd^2theta/dt^2 s gives a(theta). 


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