a = 1. ;

    GMm = 1;

    grav = -GMm/r;

    cf = GMm*a/(2*r^2);

    U = grav + cf;

    Umax = 4*GMm/(2*a);

    rmin =  .01*a;

    rmax = 3*a;

    Plot[{grav, cf, cf + grav}, {r, rmin, rmax}, PlotPoints -> 100, 
        PlotLabel -> "           Fig. 6.11.1 (F&C)", 
        AspectRatio -> 2, AxesLabel -> {"r", "U(r)"}, 
        PlotStyle -> {Dashing[{ .005,  .01}], Dashing[{ .005,  .01}], 
            Dashing[{1, 0}]}, 
        PlotRange -> {{rmin, 
              rmax}, {-Umax, +Umax}}];