Two projectiles of same mass and with same velocity are thrown at an angle 60^o and 30^o with the horizontal, then which will remain same

The width of river is 1 km. The velocity of boat is 5 km/hr. The boat covered the width of river in shortest time 15 min. Then the velocity of river stream is

A man is slipping on a frictionless inclined plane and a bag falls down from the same height. Then the velocity of both is related as

Two masses as shown in the figure are suspended from a massless pulley. The acceleration of the system when masses are left free is