you are playing with a toy in which a marble launched by a spring rolls along a track full of loop-the-loops and curves with almost no energy dissipated. you want the marble to have a speed of 0.90 m/sm/s when it arrives at the top of a loop that is 0.30 mm higher than the marble's position when you launch it. part a what initial speed must the marble have? express your answer with the appropriate units. vivi