Question

Difficulty: MediumSimple Harmonic Motion

A simple pendulum has a period of oscillation of 1.6 s1.6\text{ s} on the surface of the Earth, where the acceleration due to gravity is 10.0 m/s210.0\text{ m/s}^2. What is the period of oscillation of this pendulum when placed on a moon where the acceleration due to gravity is 2.5 m/s22.5\text{ m/s}^2?

Answer: 3.2 s

Answer

The period of oscillation of the pendulum on the moon is 3.2 s3.2\text{ s}.
The period of a simple pendulum is given by T=2πlgT = 2\pi \sqrt{\frac{l}{g}}. Because the length ll is constant, period is inversely proportional to the square root of acceleration due to gravity (T1gT \propto \frac{1}{\sqrt{g}}). Reducing the local gravity from 10.0 m/s210.0\text{ m/s}^2 to 2.5 m/s22.5\text{ m/s}^2 decreases gravity by a factor of 4, which increases the period by a factor of 4=2\sqrt{4} = 2. Multiplying the initial period of 1.6 s1.6\text{ s} by 2 yields 3.2 s3.2\text{ s}.

Step-by-Step Solution

1
Relate the period of oscillation of a simple pendulum to gravitational acceleration.
The period formula is T=2πlgT = 2\pi \sqrt{\frac{l}{g}}, showing that TT is inversely proportional to g\sqrt{g}.
The length of the pendulum ll remains unchanged.
2
Formulate a ratio comparing the pendulum's period on the moon to its period on Earth.
TmoonTearth=gearthgmoon\frac{T_{moon}}{T_{earth}} = \sqrt{\frac{g_{earth}}{g_{moon}}}
Dividing the two equations cancels the constant terms 2π2\pi and l\sqrt{l}.
3
Substitute the known numerical values and solve for TmoonT_{moon}.
T_{moon} = 1.6 \times \sqrt{\frac{10.0}{2.5}} = 1.6 \times 2.0 = 3.2\text{ s}
The ratio of gravities is 4, whose square root is 2, doubling the initial period.

Key Concept

Dependence of Simple Pendulum Period on Gravitational Acceleration
Estimated Time:1m 30s
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