Question

Difficulty: EasySimple Harmonic Motion

A simple pendulum of length ll has a period of oscillation of 2.0 s2.0\text{ s} when suspended with a bob of mass 50 g50\text{ g}. If the bob is replaced with one of mass 200 g200\text{ g} while maintaining the exact same string length, what is the new period of oscillation?

  1. 2.0 s2.0\text{ s}Answer
  2. B
    4.0 s4.0\text{ s}
  3. C
    1.0 s1.0\text{ s}
  4. D
    8.0 s8.0\text{ s}

Answer

The period of oscillation remains 2.0 s2.0\text{ s}.
The period of oscillation of a simple pendulum undergoing simple harmonic motion is given by T=2πlgT = 2\pi \sqrt{\frac{l}{g}}, where ll is the length of the pendulum and gg is the acceleration due to gravity. Because the mass of the bob does not appear in this equation, changing the mass from 50 g50\text{ g} to 200 g200\text{ g} does not alter the period. Therefore, the period remains 2.0 s2.0\text{ s}.

Step-by-Step Solution

1
Identify the formula for the period of a simple pendulum.
T=2πlgT = 2\pi \sqrt{\frac{l}{g}}
The period TT depends on the length of the pendulum ll and local acceleration due to gravity gg.
2
Analyze the dependence of period on bob mass.
The mass parameter mm does not appear in the formula T=2πlgT = 2\pi \sqrt{\frac{l}{g}}.
The period of a simple pendulum is independent of the mass of the bob.
3
Determine the new period of oscillation.
Tnew=2.0 sT_{new} = 2.0\text{ s}
Since length ll and acceleration due to gravity gg remain unchanged, the period stays 2.0 s2.0\text{ s}.

Key Concept

Independence of simple pendulum period from bob mass
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