2. 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 constant.
(v) The speed of a train is expressed in m/h.
The option (ii), (iv) and (v) are not correct.
(ii) Object can move with variable or constant speed.
(iv) Time period of pendulum depends on length of the thread. So, it is constant for a particular length.
(v) Speed oftrain is measured either in km/h or m/s not in m/h