If a stone and a pencil are dropped simultaneously in vacuum from the top of a tower, which of the two will reach the ground first ? Give reason.

The speed of a car is 72 km h^-1. Express it in m s^-1.

Express each of the following in m s ^-1 —

(a) 1 km h^-1

(b) 18 km min^-1

Arrange the following speeds in increasing order — 10 m s^-1, 1 km min^-1, 18 km h^-1.