An element for sensing local shear stress is positioned in a flat plate 0.40 meter from the leading edge. the element simply consists of a small plate, mounted flush with the wall, and the shear force is measured on the plate. the fluid flowing by the plate is air with a free-stream velocity of 30 m/s, a density of 1.2 kg/m3 and a kinematic viscosity of 1.5 × 10-5 m2/s. the boundary layer is tripped at the leading edge. what is the magnitude of the force due to shear stress acting on the element?

Tom is having a problem with his washing machine. he notices that the machine vibrates violently at a frequency of 1500 rpm due to an unknown rotating unbalance. the machine is mounted on 4 springs each having a stiffness of 10 kn/m. tom wishes to add an undamped vibration absorber attached by a spring under the machine the machine working frequency ranges between 800 rpm to 2000 rpm and its total mass while loaded is assumed to be 80 kg a) what should be the mass of the absorber added to the machine so that the natural frequency falls outside the working range? b) after a first trial of an absorber using a mass of 35 kg, the amplitude of the oscillation was found to be 10 cm. what is the value of the rotating unbalance? c) using me-3.5 kg. m, find the optimal absorber (by minimizing its mass). what would be the amplitude of the oscillation of the absorber?