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A uniform rod of length 4 m and mass 20 kg is lying horizontally on the ground. What is the work done in keeping it vertical with one of its ends touching the ground?

A. 784 J
B. 392 J
C. 196 J
D. 98 J

Answer :

Final answer:

The work done to keep a uniform rod vertical is found by calculating the change in gravitational potential energy, which comes out to 392 J(option b) in this case.

Explanation:

To determine the work done in keeping a uniform rod vertical with one end touching the ground, we can use the concept of potential energy in physics. The work done on the rod is equal to the change in gravitational potential energy when the rod is moved from horizontal to vertical position. Since the rod is uniform, its center of mass is at the middle of the rod, which is 2 m from the ground when it is vertical. The formula for gravitational potential energy is PE = mgh, where PE is the potential energy, m is mass, g is the acceleration due to gravity (approximately 9.8 m/s2), and h is the height above the reference point.

In this case: m = 20 kg, g = 9.8 m/s2, and h = 2 m (the center of mass height).

Therefore, PE = 20 kg * 9.8 m/s2 * 2 m = 392 J.

So the correct answer is B. 392 J, which is the work done to keep the rod vertical.

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