18. a bus travels from west to east with a velocity of 11.5 m/s. a marble rolls on the surface of the bus
floor with a velocity of 0.200 m/s north. what is the velocity of the marble relative to the road?

Which is the correct symbol for an isotope of iodine with 53 protons and 78 neutrons?

Glass has a hardness that is in the middle of the hardness scale. what is the hardness of glass?

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