A string going over a massless frictionless pul- ley connects two blocks of masses 4.2 kg and
3.8 kg. As shown on the picture below, the
4.2 kg block lies on a 23° incline; the coefli-
cient of kinetic friction between the block and
the incline is u= 0.23. The 3.8 kg block is
hanging in the air.
The 3.8 kg block accelerates downward
while the 4.2 kg block goes up the incline
with the same acceleration.
If gravity is constant (g=9.8), what is the acceleration of the system?

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