Question

The momentum equation is ( hofrac{Du}{Dt}=-frac{partial p}{partial x}+frac{partial au_{xx}}{partial x}+frac{partial au_{yx}}{partial y}+frac{partial au_{zx}}{partial z}+ ho f_x). Which of these statements about sign convention can be inferred from this equation?

(a) Pressure force is taken as negative

(b) Tensile force is taken as negative

(c) Pressure force is taken as positive

(d) Pressure force is unsigned

Answer 1

Correct choice is (a) Pressure force is taken as negative

Easiest explanation: When all the other forces and accelerations are positive, gradient of pressure force is negative(-(frac{partial p}{partial x})). This is possible only when pressure force is signed posititve.