Judish

A 30 meter wide canal is flowing at the rate of 20 m/min. A boy can swim at the rate of 25 m/min in still water. The time taken by him to cross the canal perpendicular to the flow is

Two transparent media F and G are separated by a plane boundary. The speed of light in medium F is 2.0x108 m/sec and in medium G is 2.5x108 m/sec. The critical angle for which a ray of light from F to G is totally internally reflected is