Distance between the centres of two stars is `10a`. The masses of these stars are `M` and `16 M` ans their radit a nd `2a` respectively. A body of mass `m` is fired straight from the surface of the larger star tpwards the surface of the smaller star. What should be its minimum intial speed to reach the surface of the smaller star? Obtain the expression in terms of `G`, `M` and a.