Question

Difficulty: MediumMeasurement of Time

A ticker-tape timer operates at an alternating current frequency of 50 Hz50\text{ Hz}. During a mechanics experiment, a paper tape pulled through the device records a section containing 1111 consecutive dots. What is the total time elapsed for this section of the tape?

  1. 0.20 s0.20\text{ s}Answer
  2. B
    0.22 s0.22\text{ s}
  3. C
    0.55 s0.55\text{ s}
  4. D
    550 s550\text{ s}

Answer

The total time elapsed for this section of the tape is 0.20 s0.20\text{ s}.
The period of a 50 Hz50\text{ Hz} ticker-tape timer is T=150 Hz=0.02 sT = \frac{1}{50\text{ Hz}} = 0.02\text{ s}. A sequence of 1111 consecutive dots contains 1010 time intervals (111=1011 - 1 = 10). Multiplying 1010 intervals by 0.02 s0.02\text{ s} yields 0.20 s0.20\text{ s}.

Step-by-Step Solution

1
Determine the time interval (period) between consecutive dots recorded by the timer.
T=1f=150 Hz=0.02 sT = \frac{1}{f} = \frac{1}{50\text{ Hz}} = 0.02\text{ s}
The ticker-tape timer makes one dot every period TT of the operating frequency.
2
Calculate the number of intervals (spaces) between the first and last dot in the sequence.
\text{Number of intervals } n = N - 1 = 11 - 1 = 10
Time elapses between dots, so NN dots define N1N-1 spaces.
3
Multiply the number of intervals by the time period of one interval to get total time elapsed.
t = 10 \times 0.02\text{ s} = 0.20\text{ s}
Total duration is the product of the number of spaces and the duration of a single space.

Key Concept

Ticker-Tape Timer Period and Time Interval Calculation
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