A rock of mass m is dropped to the ground from a height h. A second rock, with mass 2m, is dropped from the same height. Ignoring air resistance, when the second rock strikes the ground, its kinetic energy is.1. Twice that of the first rock2. Four times that of the first rock3. The same as that of the first rock4. Half as much as that of the first rock5. Impossible to determine

Gravity is the universal force of attraction between a free-falling objects and the Earth. The objects falling from the same height will have the same speed.

The correct answer is:

Option 1.  Twice that of the first rock.

Air resistance has been ignored in the given situation. The rocks when dropped from the same height will have the same speed and acceleration. The kinetic energy of rocks with different masses can be given as:

From the above equation of kinetic energy, it can be predicted that the speed is same for the rocks. The kinetic energy is directly dependent on the mass, such that the rock with a mass of 2m will have more kinetic energy.

Thus, the kinetic energy of the rock with a mass of 2m will be twice that of the first rock.

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1. Twice that of the first rock.

Explanation:

It is first important to realize that without air resistance, all objects dropped from the same height will travel at the same speed. This is because the acceleration of each object is the same, since gravity acting on each object is the same.

This means that the first and second rock strike the ground at the same speed, since they were released from the same height.

Kinetic energy = 0.5 * mass * Speed^2

Since the speed in the above equation is the same for both objects, the kinetic energy just depends on the mass of the object. If mass is increases 2 times in the above equation, Kinetic energy will also increase two times.

Thus, the second rock's kinetic energy is twice that of the first rock.

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