Answer:
Neglecting air resistance, the only force acting on a projectile is gravity.
This force causes the object to accelerate.
Explanation:
As a projectile moves upward, there is a downward force and a downward acceleration due to force of gravity. That is, as the object is moving upward, force of gravity acting on the projectile is causing a steady slowing down of the projectile.
Hence, Gravity is the downward force upon a projectile that influences its vertical motion and causes the parabolic trajectory that is characteristic of projectiles.
From Newton's law of motion, it suggest that force is required to cause an acceleration and not motion. Therefore, force of gravity causes the object to accelerate downwards.
Answer:
The answer is 0.83 seconds.
Explanation:
The formula of free fall is following:

Where g=9.8 m/s^2 and t=2 seconds, the rock takes:

19.6 meters. This is the half distance of the cliff. The whole distance is 39.2 meters. So it takes:

2.83 second to fall down completely. The rock takes the second half of the cliff in 0.83 seconds
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