The velocity of the player is - 0.05 m/s.
From the law of conservation of linear momentum, the momentum after collision is equal to the momentum before collision. We can see that the initial momentum of the system is zero.
Hence;
0 = (0. 51 kg × 6 m/s) + 59 kg v
0 = 3.06 + 59v
v = -3.06/59
v = - 0.05 m/s
The negative sign means that the velocity of the player is opposite that of the ball.
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