Yes it is of interest, but asking adults on this forum they can well ask what are the objectives and constraints? If the objective is as far as possible then tigertiger's post #3 raises a most valid point, and #14 may well favour the 'heavier' child , and in this particular project how BIG can the elastic band be, or how many?
It may well be an interesting activity for a child, especially in today's world of mostly 'digital' entertainment, but if the child cannot design his own solution to the problem posed- but not necessarily construct it( which could well pose risks)-- and then have it analysed as to its merits and impracticalities along with the other pupil's efforts, then how much will he/she actually learn? To do this sort of thing properly surely the children would each need to have a teacher selected/matched pile of materials to design and construct their ''rocket'' to prove their ideas and construction?
Trevor