measurement-of-time MCQs for UPSC Prelims

25 practice questions on measurement-of-time from the Measurement of Time and Motion section of the UPSC Prelims syllabus. 25 come with a written explanation. Try the sample set below - the answer stays hidden until you ask for it.

8 Easy 12 Medium 5 Hard

Sample questions

Q1
medium

Two statements about time units are given. (i) $1$ hour $= 3600\ \text{s}$. (ii) $1$ minute $= 100\ \text{s}$. Which of these is correct?

  1. A Only (i)
  2. B Only (ii)
  3. C Neither (i) nor (ii)
  4. D Both (i) and (ii)
Show answer and explanation

Correct answer: A - Only (i)

An hour holds $60$ minutes of $60\ \text{s}$ each, which gives $3600\ \text{s}$, so the first statement is right. A minute holds $60\ \text{s}$ and not $100$, because time is not counted in hundreds, so the second statement is wrong.

Q2
easy

The time period of a simple pendulum is

  1. A the time taken to complete ten oscillations
  2. B the number of oscillations made in one second
  3. C the length of the thread of the pendulum
  4. D the time taken to complete one oscillation
Show answer and explanation

Correct answer: D - the time taken to complete one oscillation

The time period is the time for a single complete to and fro swing. Timing ten swings is a way of measuring it accurately, but the total is ten periods, not one. The number of swings per second is a different quantity, and the thread length is a distance, not a time.

Q3
hard

Which of these would work best as a natural clock, and why?

  1. A The phases of the Moon, because they repeat in a fixed cycle
  2. B The number of birds seen in a garden, because birds visit every morning
  3. C The movement of clouds, because they drift across the sky each day
  4. D The height of a growing plant, because plants grow every day
Show answer and explanation

Correct answer: A - The phases of the Moon, because they repeat in a fixed cycle

The Moon goes through its full set of phases in the same number of days every time, so the cycle can be counted like a clock. Clouds drift at speeds that change from hour to hour, plants grow by different amounts depending on water and weather, and the number of visiting birds varies from day to day.

Q4
medium

A sand clock measures time by using

  1. A the number of grains counted as they fall through
  2. B the fixed time the sand takes to run from the upper bulb into the lower one
  3. C the change in the colour of the sand as it falls
  4. D the weight of the sand collected in the lower bulb
Show answer and explanation

Correct answer: B - the fixed time the sand takes to run from the upper bulb into the lower one

The same quantity of sand always takes the same time to trickle through the narrow neck, so turning the clock over marks off equal intervals. The weight of sand tells us how much there is, not how long it took, the sand does not change colour, and counting individual grains is impossible.

Q5
easy

The best instrument for measuring the time a runner takes to finish a $100\ \text{m}$ race is

  1. A a stopwatch
  2. B a sand clock
  3. C a wall clock
  4. D a calendar
Show answer and explanation

Correct answer: A - a stopwatch

A stopwatch can be started and stopped at will and reads to a fraction of a second, which is what a short race needs. A wall clock is hard to read to the second, a calendar measures days, and a sand clock runs for one fixed interval that cannot be adjusted.

Q6
easy

One complete oscillation of a pendulum means that the bob goes

  1. A once round a complete circle
  2. B from one extreme position to the other only
  3. C from the middle to one extreme position only
  4. D from one extreme position to the other and back again
Show answer and explanation

Correct answer: D - from one extreme position to the other and back again

An oscillation is finished only when the bob returns to the point it started from, moving the same way as before, which means one full to and fro swing. Going across just once is half an oscillation, and going from the middle to one side is only a quarter. A pendulum swings along an arc rather than round a circle.

Q7
medium

A pendulum completes $20$ oscillations in $30\ \text{s}$. Its time period is

  1. A $600\ \text{s}$
  2. B $0.67\ \text{s}$
  3. C $1.5\ \text{s}$
  4. D $50\ \text{s}$
Show answer and explanation

Correct answer: C - $1.5\ \text{s}$

The time period is the total time divided by the number of oscillations, so it is $30 \div 20 = 1.5\ \text{s}$. Dividing the other way round gives $0.67\ \text{s}$, which is the number of swings each second instead. Adding the two numbers gives $50$ and multiplying them gives $600$, and neither operation has any meaning here.

Q8
medium

A train journey lasts $9000\ \text{s}$. In minutes, this is

  1. A $250\ \text{min}$
  2. B $90\ \text{min}$
  3. C $150\ \text{min}$
  4. D $180\ \text{min}$
Show answer and explanation

Correct answer: C - $150\ \text{min}$

Dividing by the $60\ \text{s}$ in a minute gives $9000 \div 60 = 150\ \text{min}$. Dropping the last two zeros gives $90$, which uses a factor of $100$ instead of $60$. The values $250$ and $180$ do not follow from any correct conversion.

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