Kinetic energy (KE) is given by the formula:
\[ KE = \frac{1}{2} mv^2 \]
where \( m \) is the mass of the object and \( v \) is its velocity just before it hits the water. When all four objects are dropped from the same height, they will fall under the influence of gravity (ignoring air resistance), and they will all have the same velocity just before impact if we assume they are dropped simultaneously.
Since the kinetic energy depends on mass and all the objects will have the same velocity at the moment of hitting the water, the object with the greatest mass will have the greatest kinetic energy.
From the table:
- Table tennis ball: 2.7 grams
- Baseball: 147.0 grams
- Small rock: 248.2 grams
- Penny: 2.5 grams
The small rock has the greatest mass (248.2 grams), so it will have the greatest kinetic energy when dropped from a height of 2 meters.
Therefore, the answer is:
small rock
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