Answer
The stone applies a force with a magnitude of $19.6~N$ on the man's hand.
Work Step by Step
Since the stone moves with a constant velocity, the net force on the stone must be zero. Then the man's applied force must be equal in magnitude to the stone's weight. We can find the force $F$ that the man applies:
$F = mg = (2.0~kg)(9.80~m/s^2) = 19.6~N$
By Newton's third law, the stone applies a force with a magnitude of $19.6~N$ on the man's hand.
