An exact solution to the unsteady free convection flow of viscous incompressible fluid, in the presence of foreign mass, past an impulsively started infinite vertical isothermal plate in a rotating fluid, has been derived by Laplace-Transform technique. Axial and transverse velocity profiles are shown on graphs and numerical values of skin friction are listed in a table. It is observed that the non dimensional rotational parameter Rc increases there is fall in axial velocity profiles for all prandtl numbers because the coriolis forces oppose the fluid flow , hence the motion gets slow down . As Rc < 10 -3 the flow field becomes unstable and flow is converted to the turbulent flow for all Prandtl numbers (i.e. Pr = .71 for air when Ma<<1 and Pr = 7 for water). The flow of water may become unstable at large values of time t. Increase in Schmidt number leads to decrease in axial velocity for air and water. The diffusion parameter ,N, increases leads to rise in axial velocity because the buoyancy flow forces assist the flow and the transverse skin friction increases for both air and water, the axial skin friction decreases for air and increases for water.

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