Numerical Problems Based on Measurement of Time for Class 11 Physics

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Home CBSE Class 11 Physics Numerical Problems Based on Measurement of Time for Class 11 Physics

Numerical Problems on Time Measurement

Class 11 Physics · Units and Measurements
SQ

Time Scales and Accuracy Practice Set

Apply dimensional analysis and unit conversions
Ch 2 · Units and Measurements
1
Find the number of times the human heart beats in the life of 60 years of a man, assuming that the heart beats once in $0.8\text{ s}$.
Answer $2.3668 \times 10^9\text{ beats}$ 📝
Detailed Solution

Total life span of the man, $T = 60\text{ years}$.

We convert this time into seconds (considering $365.25\text{ days}$ in a year to account for leap years):

$$T = 60 \times 365.25 \times 24 \times 60 \times 60\text{ s}$$
$$T = 1,893,456,000\text{ s} = 1.893456 \times 10^9\text{ s}$$

Time taken for one heart beat, $t = 0.8\text{ s}$.

Total number of heart beats ($N$) is the total time divided by the time per beat:

$$N = \frac{T}{t} = \frac{1.893456 \times 10^9}{0.8}$$
$$N = 2,366,820,000 = 2.3668 \times 10^9\text{ beats}$$
2
Two atomic clocks allowed to run for average life of an Indian (say, 70 years) differ by $0.2\text{ s}$ only. Calculate the accuracy of standard atomic clock in measuring a time interval of $1\text{ s}$.
Answer 1 part in $10^{10}$ 📝
Detailed Solution

Total time elapsed, $T = 70\text{ years}$.

Converting this time into seconds:

$$T = 70 \times 365.25 \times 24 \times 60 \times 60\text{ s}$$
$$T \approx 2.209 \times 10^9\text{ s}$$

The difference (error) in the clocks over this entire duration is $\Delta T = 0.2\text{ s}$.

The accuracy in measuring a time interval of $1\text{ s}$ is the error per second:

$$\text{Error per second} = \frac{\Delta T}{T} = \frac{0.2}{2.209 \times 10^9}$$
$$= \frac{1}{11.045 \times 10^9} \approx \frac{1}{10^{10}}$$

Thus, the accuracy of the standard atomic clock is approximately $1\text{ s}$ in $10^{10}\text{ s}$.

3
Age of the universe is about $10^{10}\text{ years}$ whereas the mankind has existed for $10^6\text{ years}$. For how many seconds would the man have existed if age of universe were 1 day?
Answer $8.64\text{ s}$ 📝
Detailed Solution

Given the actual age of the universe $T_u = 10^{10}\text{ years}$ and the actual time mankind has existed $T_m = 10^6\text{ years}$.

The fraction of the universe’s life that mankind has existed is:

$$\text{Fraction} = \frac{T_m}{T_u} = \frac{10^6}{10^{10}} = 10^{-4}$$

If the scaled age of the universe is exactly $1\text{ day}$, we first convert $1\text{ day}$ into seconds:

$$1\text{ day} = 24\text{ hours} = 24 \times 60 \times 60\text{ s} = 86,400\text{ s}$$

The scaled time for mankind’s existence is the same fraction of this new universe age:

$$\text{Scaled mankind existence} = 10^{-4} \times 86,400\text{ s}$$
$$= 8.64\text{ s}$$

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