Aweight of 20.0 n hangs motionless from a spring, with a spring constant of 65.0 n/m. how far is the spring stretched from its original length?

0.130 m
0.308 m
0.769 m
3.25 m

Aparticle is moving around in a circle and its position is given in polar coordinates as x = rcosθ, and y = rsinθ, where r is the radius of the circle, and θ is in radians. from these equations derive the equation for centripetal acceleration.