Double Integral Mistake with Parametric Equation

Question

I'm trying to figure out the mass of an object bounded by $y=0$ and $y=\sqrt{1-x^2}$ the density at a given point is proportional to its distance from the origin; $\rho(x,y) = kxy$. So I set it up like this: $$\int_{0}^{\pi}\int_{0}^{1}kr^3\sin(\theta)cos(\theta)\,\mathrm{d}r\mathrm{d}\theta$$ Unfortunately I'm getting 0, I think this is because my density function is becoming negative in the second quadrant. I know that using the absolute value in my density function will probably solve my problem but how do I do that?