A jet-fighter pilot, wishing to experience weightlessness conditions, enters a parabolic trajectory closely approximating that of a projectile in free-fall. His aircraft must fly at a minimum speed of 400 km/hr to keep control, and he should not exceed 600 km/hr so as not to suffer a black-out when he pulls out of the trajectory at the end. There is no wind and air resistance can be compensated by the engine. In order to be weightless as long as possible, he should enter the parabola at an upward angle (with respect to the horizontal ground) of
(a) 33.7°.
(b) 41.8°.
(c) 56.3°.
(d) 48.2°.