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A positive charge Q = 1400.00 C is uniformly distributed over the volume of a sphere of radius R = 10.00 m. Suppose a spherical cavity of radius R/2 is cut out of the solid sphere, the center of the cavity being a distance R/2 from the center of the original solid sphere (see figure). The cutout material and its charge are discarded. What is the magnitude of the electric field produced by this new charge distribution at point P, a distance r = 24.50 m from the center of the original sphere?
(picture attached)
I have calculated the Efield of the point using the equation E=kQ/r^2. I first did this using the radius 24.5m. I then used the radius 24.5m5m=19.5m. I then subtracted these two Efield calculations and get the wrong answer. E(r)  E(rR/2)
What am I doing wrong?
(picture attached)
I have calculated the Efield of the point using the equation E=kQ/r^2. I first did this using the radius 24.5m. I then used the radius 24.5m5m=19.5m. I then subtracted these two Efield calculations and get the wrong answer. E(r)  E(rR/2)
What am I doing wrong?
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