Question 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 not constant. (v) The speed of a train is expressed in m/h.

Answer:(i) Correct Second is the SI unit of time. (ii) Not correct An object can move with constant or variable speed. (iii) Correct The distance between two cities can be very large. Since kilometre is a bigger unit of distance, the distance between two cities is measured in kilometres. (iv) Not correct Time period of a pendulum depends on the length of the thread. Hence, it is constant for a particular pendulum. (v) Not correct The speed of a train is measured either in km/h or in m/s.