28. someone throws a rubber ball vertically upward from the roof of a building 8.00 m in height. the ball rises,

then falls. it just misses the edge of the roof, and strikes the ground. if the ball is in the air for 3.00 s, what

was its initial velocity? (disregard air resistance.)

Consider a uniformly charged ring in the xy plane, centered at the origin. the ring has radius a and positive charge qdistributed evenly along its circumference. a)what is the direction of the electric field at any point on the z axis? . b)what is the magnitude of the electric field along the positive z axis? use k in your answer, where k=14πϵ0. d)the ball will oscillate along the z axis between z=d and z=−d in simple harmonic motion. what will be the angular frequency ω of these oscillations? use the approximation d≪a to simplify your calculation; that is, assume that d2+a2≈a2. express your answer in terms of given charges, dimensions, and constants