Since you use the term "drag coefficient" can we assume that you know what it means? According to Wikipedia, the drag coefficient is given by $\displaystyle c_d= \frac{2F_d}{\rho u^2A}$ where $\displaystyle c_d$ is the drag coefficient, $\displaystyle F_d$ is the drag force, $\displaystyle \rho$ is the density of the fluid, u is the speed through the fluid, and A is the cross section area. You are asked for the drag force so solve for that: $\displaystyle F_d= \frac{c_d\rho u^2A}{2}$. You are given that A= 400 square cm. and $\displaystyle c_d= 0.6$. You will need to look up the density of air and water and calculate u, the speed of an object moving at 1000 rev/min around a circle of radius $\displaystyle 10 sin(120^o)$.
