Question

Which of the following methods of measurement of time is suitable for a race?
A) Stopwatch
B) Wall clock
C) Simple pendulum
D) Reflection of an object by sun rays

Answer 1

Hint: We have to keep in mind that during a race, even a fraction of a second can make a huge difference in decision-making. Also, the precision of the device plays a crucial role too. So to reach the answer, we have to carefully analyze all the given instruments and find their least count. Also, we have to try to figure out which of these instruments has the least error while measuring the time.

Complete answer:
In physics, time is used to measure, calculate or compare the duration of events or a sequence of events. Time can be measured using different devices like wall clocks, stopwatches, sundials, and so on.
But, during a race, even a difference of a fraction of a second can make someone a winner and someone a loser. So, an instrument with high precision and lower least count should be used. The wall clock has a least count of one second i.e. it cannot measure time below one second. Also, there will be an error in measuring time due to the wear and tear of the machinery or the battery. The simple pendulum and reflection of an object by sun rays gives a perspective of time but cannot measure the actual time. Therefore they can’t be used in a race and hence stopwatch is used in a race due to its higher precision and the least count of a fraction of a second.
Hence, option (A) is correct.

Note:
Before the invention of clocks, sundials are used in ancient times to measure time. It is a device that tells the time by using the apparent position of the sun. It contains a rod-like structure called gnomon and a dial attached to it. As the earth moves around the sun, the position of the sun changes, and hence the shadow cast by the gnomon falls on the dial and changes accordingly.