Passage IV

One type of torsion pendulum consists of a wire tied to a rod with a disk on each end. The pendulum is suspended from a support (see Figure 1).

The rod is turned, twisting the wire, and then released, causing the rod and disks to oscillate (twist back and forth) in a horizontal arc, as shown in the top views in Figure 2.

The period is the time required for the rod to complete 1 round trip. Tables 1-3 give the periods of torsion pendulums made with identical wires and various disk masses, rod masses, and rod lengths.

20. Consider a torsion pendulum made from one of the wires mentioned in the passage and a 15 cm rod with one 3 g disk on each end. Based on the data in Tables 1-3, the period of this pendulum will be closest to 10.3 sec if the rod's mass is which of the following?

Answer and Explanation

Your Answer is

Correct Answer is H

Explanation

Looking at the three tables, the value closest to 10.3 is in Table 3. The period corresponding to the rod length of 15 cm & the mass per disk of 3 g is 10.9 sec. By comparing the three tables, we can see that the larger the rod mass, the larger the period. Therefore, when the period is 10.3, the corresponding rod mass should also be smaller than the 30 g given in Table 3, but larger than the 20 g given in Table 2. So option H is reasonable.