The length of a second's pendulum, at a place where the acceleration due to gravity is 9.8 m/s squared, is nearly
- A.1 metre
- B.2 metres
- C.0.5 metre
- D.9.8 metres
Correct answer
Explanation
The correct answer is A, one metre. A second's pendulum is one whose time period is exactly two seconds, so that each swing from one side to the other takes one second. Putting T equal to two in the formula gives a length of about 99.4 centimetres, which is taken as nearly one metre. Option B is wrong because a two-metre pendulum would have a period of about 2.8 seconds, since the period grows as the square root of the length. Option C is wrong because a half-metre pendulum has a period of about 1.4 seconds. Option D is wrong because 9.8 is the value of g in metres per second squared and not a length; mixing up the two is the trap in this question. Remember that a second's pendulum is shorter where g is smaller, as on the moon.
Read the full article: Oscillations: Simple Harmonic Motion and Pendulum Notes
Practice Questions
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- A.Maximum
- B.Zero
- C.Minimum
- D.None of these
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- A.10 m/s
- B.5 m/s
- C.8 m/s
- D.15 m/s
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- A.The length of the pendulum
- B.The mass of the bob
- C.The acceleration due to gravity
- D.All of these
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- A.Four times
- B.Two times
- C.Half
- D.One fourth
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- A.Decrease
- B.Increase
- C.Remain the same
- D.Become zero
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Read the full explanation →