A body of mass 6 kg accelerates from 6 m/s to 18 m/s in 3 seconds due to the application of a force on it. Calculate the magnitude of this force (in N).
A man standing on the bank of river observes that the angle subtended by a tree on the opposite bank is 60°. When he retires 36 m from the bank, he finds that the angle is 30°. The breadth of the river is