1. The problem statement, all variables and given/known data A 100g (0.1kg) rock is attatched to a 1.0m rope and spun around in a circle with a period of rotation of 1.0s. What is the Radius of the circle that it forms? 2. Relevant equations Fc = (mV^2) / r V= (2∏r/T) LCosθ = r 3. The attempt at a solution Im quite stick here, as Im not sure how I could ever find r without knowing the θ of the circle. First thing I tried was making a triangle like so: Illustration in 2D Im going to start with the simple equation TCosθ = Fc. We also know that (mV^2)/r = Fc. If you put those 2 equations together, you get TCosθ = (mV^2)/r. This leaves us with the equation: TCosθ = (mV^2)/ r Furthurmore, we know that V = 2πr/P (Where P is period, should normally be T but theres Tension in this equation, so ill just do P) TCosθ = m (2πr/P)^2 / r The period of rotation is 1, so the equation simplifies again to: TCosθ = m (2πr)^2 / r We can also sub r in to the formula we just moved in. TCosθ = m (2π (Cosθ)^2) / Cosθ From here, we can make the equation: T = (m (2π) ^2 * (Cosθ)^2) / (Cosθ)^2 (Correct? Im not sure if thats logical) Now the (Cosθ)^2 can cancel out, making: T = m (2π)^2 Sub in the values, we have T = (0.1)(2π)^2 = 0.4π^2 We now know Tension, Which we can use in the triangle. Triangle illustration If I use Sin, I can find that the angle is 14.37321*. We can use this θ in the equation LCosθ = r (1)(Cos14.37321) = r r = 0.97 m. Is that correct?