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Christy has a grandfather clock with a pendulum that is \(1.000 \mathrm{m}\) long. (a) If the pendulum is modeled as a simple pendulum, what would be the period? (b) Christy observes the actual period of the clock, and finds that it is \(1.00 \%\) faster than that for a simple pendulum that is \(1.000 \mathrm{m}\) long. If Christy models the pendulum as two objects, a \(1.000-\mathrm{m}\) uniform thin rod and a point mass located \(1.000 \mathrm{m}\) from the axis of rotation, what percentage of the total mass of the pendulum is in the uniform thin rod?

Short Answer

Expert verified
The formula for the period (T) of a simple pendulum is T = 2\pi\sqrt{\frac{l}{g}}, where "l" is the length of the pendulum and "g" is the acceleration due to gravity. This formula is used to calculate the period of an ideal simple pendulum under the influence of gravity.

Step by step solution

01

Calculate the period of a simple pendulum

For a simple pendulum, the period T is given by the formula: T = 2\pi\sqrt{\frac{l}{g}} where l is the length of the pendulum and g is the acceleration due to gravity (9.81 m/s²). Plug in the given length (1.000 m) and calculate the period: T = 2\pi\sqrt{\frac{1.000}{9.81}}.
02

Calculate the actual period

The actual period of the grandfather clock is 1% faster than that of a simple pendulum. So, multiply the calculated period in step 1 by 0.99 to get the actual period: Actual T = 0.99 * T.
03

Model the pendulum as two objects

The pendulum's mass is distributed between the uniform thin rod and the point mass at its end. The moment of inertia of a uniform thin rod rotating about its end is given by I_rod = \frac{1}{3} m_rod * L^2. The moment of inertia of a point mass at the distance L from the axis is given by I_mass = m_mass * L^2.
04

Determine the percentage of mass in the uniform thin rod

The total moment of inertia of this pendulum is I_total = I_rod + I_mass. We know that for any physical pendulum, the period is given by T = 2\pi\sqrt{\frac{I}{mgr}}, where r is the distance from the axis to the center of mass of the pendulum. From step 2, we have the actual period, T, so we can use this to solve for I_total: I_total = \left(\frac{T^2 g r}{4\pi^2}\right). We need to find the center of mass, r. For the uniform thin rod, the center of mass is halfway along its length, at 0.5 m. The point mass's center of mass is at its location, 1.000 m. The combined pendulum’s center of gravity can be found by considering the two masses in parallel: r = \frac{m_rod * 0.5 + m_mass * 1.0}{m_rod + m_mass}. Plug in the moments of inertia and the center of mass values, and solve the equation for I_total. Once you have I_total, find the fraction of the total mass of the pendulum in the uniform thin rod, which is m_rod / (m_rod + m_mass). Finally, multiply this fraction by 100 to get the percentage.

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