Ex. 1. an infinite mass of jluid is acted on by aforce lr per unit mass directed to the origin. f initially the jhuid is at rest and there is a cavity in the jo

Ex. 1. An infinite mass of jluid is acted on by aforce lr per unit mass directed to the origin. f initially the Jhuid is at rest and there is a cavity in the Jorm of the sphere r= c in i, show that the cavity will be filled up after an interval of time (2/5) [Kanpur 1999, 2009; Meerut 2005; I.A.S. 2003]