Question:
Which of the following are not correct?

(i) The basic unit of time is second.
(ii) Every object moves with a constant speed.
(iii) Distances between two cities are measured in kilometres.
(iv) The time period of a given pendulum is not constant.
(v) The speed of a train is expressed in m/h.

Answer:

(i) Correct The SI (Systeme international) unit of time is second according to the metric scale.

(ii) Not correct Every object has its own speed and variable from others. For example; in comparison to: a running horse and a moving tortoise.

(iii) Correct The distance between two cities is very large so we cannot measure it in meters; so kilometres is a bigger unit thus it is used to measure the distance between the two cities.

(iv) Not correct The time period of the pendulum is constant, because it shows to and froth motion which is an example of periodic motion (occurs in the same interval of time).

(v) Not correct We cannot express the speed of train in m/h because meter is a too short unit for measuring the distance covered by the train per hour. So, we use km/h to measure the distance covered by train.

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