Force between two identical bar magnets whose centers are ‘r’  meter apart is 6.4 N , when their axis are in the same line. If the separation is increased to 2r meter, the force between them is reduced to

Two bar magnets placed along same axis/line at distance  (between their centers) exert a force on each other F∝M1M2r4  When M1 & M2 are magnetic moments⇒F1F2=r2r14  ⇒F2=r1r24.F1⇒F2=116×F1 ⇒F2=6.416=0.4 N .