A sphere of density `rho` falls vertically downward through a fluid of density `sigma`. At a certain instant its velocity is u. The terminal velocity of the sphere is `u_0`. Assuming that stokes’s law for viscous drag is applicable, the instantaneous acceleration of the sphere is found to be `beta(1-(sigma)/(rho))(1-u/(u_(0)))`. here `beta` is in an integer. find `beta`.