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A 5.00-kg mass is on the end of a massless rigid rod of length l=70.0cm which pivots freely about the other end. The mass is moving in a verticle circle. When the rod makes an angle of theta=55.0° with the horizontal, the speed of the mass is 1.60 m/s.

a) calculate the magnitude of the force exerted on the mass by the rod.

I already calculated this to be 21.9N and this is correct.

b) (WHERE I NEED HELP) Calculate the speed of the mass at the highest point of the circle.

Now I know I need to write the forces for this point... F = mv²/L - mg

but this equation gives me 2 unknowns, where do I get a value to sub for F (the force exerted by the rod)...or is there some simplifying step I'm missing here...

please help,

thanks.

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# Homework Help: Circular Motion Fun!

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