uniform motion help?

Question

The doctor and Clara, who are 210 meters apart, start walking towards each other at 1:00pm at rates of 1.5 m/s and 2m/s, respectively. At what time will they meet?

Answer 1

The easiest way to analyze problems like this one is via the concept of closing speed.   The doctor and Clara are closing the distance between then at the rate of  1.5 m/s + 2 m/s =  3.5 m/s.     The distance between them is decreasing at this rate.    The distance between them will change from 210 m to 0 m (i.e. by 210 m) in some time t.   By the rate equation  210 =  3.5 x t    ,   so t =  60 sec = 1 minute.    Therefore they will meet at 1:01pm.