The horizontal acceleration of the rock 2 is zero.
The given parameters;
initial velocity of Rock 1 = 0
initial horizontal velocity of Rock 2 = 5 m/s
An object falling under the influence of gravity experiences acceleration due to gravity which is always directed vertically downwards.
An object moving horizontally is not affected by gravity and thus will experience no acceleration in the horizontal direction.
Thus, we can conclude that the horizontal acceleration of the rock 2 is zero.
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