1. The problem statement, all variables and given/known data Problem 1. A block having mass m and charge +Q is connected to an insulating spring having force constant k. The block lies on a frictionless, insulating horizontal track, and the system is immersed in a uniform electric field of magnitude E directed as shown in Figure P25:7. The block is released from rest at a moment when the spring is unstretched (that is, when x = 0). (a) By what maximum amount does the spring expand? (b) What is the equilibrium position of the block? Problem 2. Consider a closed surface S in a region of gravitational field g. Gauss’s law for gravitation tells us that the gravitational flux through surface S is linearly proportional to the total mass min occupying the volume contained by S. More specifically, Gauss’s law states that (closed integral)g x da = -4Gmin : Note that g here is the total electric field, due to mass sources both inside and outside S. The value of G, the gravitational constant, is about 6.673 x10-11 N m2/kg2. (a) Earth’s volume mass density, at any distance r from its center, is given approximately by the function p = A-Br=R, where A = 1.42 x 104 kg/m3, B = 1.16 x 104 kg/m3, and Earth’s radius R = 6.370 x 106 m. Calculate the numerical value of Earth’s mass M. Hint: The volume of a spherical shell, lying between radii r and r + dr, is dv = 4(pie)r2dr. (b) Determine the gravitational field inside Earth. (c) Using the result of part b, determine the gravitational field magnitude at Earth’s surface. 2. Relevant equations 3. The attempt at a solution 1.Arbitrarily choose V = 0 at 0. Then at other points V= −Ex and Ue =QV=−QEx. Between the endpoints of the motion, (K +Us+ Ue)i = (K+ Us +Ue)f 0+0+0=0+(1/2)kx2max −QExmax so xmax = (2QE)/k At equilibrium, ΣFx= −Fs+Fe= 0 or kx =QE . So the equilibrium position is at x = QE/k Problem 2. I have no clue at where to begin, or what equations to use. Any help is appreciated.