In the diagram, a force of 20 newtons is applied to a block. The block is in dynamic equilibrium. What is the magnitude and direction of the frictional force? A. 20 newtons in the direction of the applied force
B. 20 newtons opposite to the direction of the applied force
C. 20 newtons perpendicular to the direction of the applied force
D. 20 newtons in two directions, perpendicular and in the direction of the applied force
E. No friction is acting on the block.

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