Test: Motion & Time - UPSC

Change in position of a body with respect to its surrounding is called as motion.

Sundials were used for measuring time in earlier days on the basis of shadow position.

The speed of vehicle at particular point of time is recorded by speedometer fitted on the dashboard of vehicle.

The basic unit of distance is metre (m). The basic unit of time is second (s). Therefore, the basic unit of speed is m/s.

So option D is the correct answer. 

One hour = 60 minute and one minute = 60 seconds. Therefore, one hour= 60 x 60 = 3600 seconds.

Atomic watches are the most accurate of all wristwatches. An atomic watch is a wristwatch that is radio-controlled to keep the most accurate time on earth. An atomic watch never needs to have its time or date set/adjusted because it receives a low frequency radio signal each night that keeps it perfectly synchronized with the US atomic clock in Colorado.

S.I. unit of time is second.

Speed time graph is straight line parallel to x-axis for uniform motion of the body.

The rate of change in position of a body is called speed. S.I. unit of speed is meter per second.

 We know , 

1km/h=5/18m/s
72km/h=72×5/18m/s
=4×5m/s
=20m/s.