Aloop-the-loop has a circular arc, with a marble that can run along a track and traverse the entire inside of the loop. when the marble is precisely at the top of the inside loop, it has its minimum speed. ~v what do we know about the direction of the net force on the marble at this point, the top of the loop? a. the net force is instantaneously in the direction of the marble’s velocity b. the net force is instantaneously in the opposite direction to the marble’s velocity ~v. c. the net force is vertically downward. d. the net force is vertically upward

1. what is the relationship between wavelength and the penetrating power of an electromagnetic wave? a) the penetrating power has no relationship to the wavelength. b) the penetrating power increases as the wavelength increases. c) the penetrating power decreases as the wavelength increases. d) the penetrating power decreases as the wavelength decreases. 2. as ice melts and turns into water, the speed of sound through the material would most likely do what? justify your answer. a) the speed would not change because the material is always water. b) the speed of sound would increase because the density of water is less than that of ice. c) the speed of sound would increase because energy is added to ice in order to make it melt. d) the speed of sound would decrease because sound travels faster through solids than liquids. 3.which of these waves need a medium to travel through? a) sound b) x-rays c) infrared rays d) visible light