If you only want to get rid of the part where sin(x) is negative you can use
maxima.plot2d(sqrt(sin(x)),[x,0,10])
(write this in sage - it has a maxima interface built in).
However, since the values of sqrt(sin(x)) in these places are complex, a possibly better visualization of it is
complex_plot(sqrt(sin(x)), (0, 10), (-1, 1))
This is a strip around the range you are interested in. Here is an explanation of the output, from sage manual:
The magnitude of the output is indicated by the brightness (with zero being black and infinity being white) while the argument is represented by the hue (with red being positive real, and increasing through orange, yellow, ... as the argument increases).
This page demonstrates and explains some complex plots.