A car travels along a straight line for the first half time with speed 50 km/hr and the second half time with a speed 60 km/hr the average speed of the car is.

Let the total time ‘t’ hr

First half time t/2 hr
Second half time t/2 hr
Distance travelled by a car first half time,  $velocity=\frac{dis\tan ce}{time}\Rightarrow S_1=v_1{t}_1=50\frac{t}{2}=25tkm$
 Similarly  $S_2=v_2{t}_2=60\times \frac{t}{2}=30tkm$
 Average speed   $=\frac{S_1+S_2}{t}=\frac{25t+30t}{t}=\frac{55t}{t}=55km/hr$

conversion:  1km=1000 meter

                    1hour=60x60 second
Average speed  $=\frac{55\times 1000}{60\times 60}=15.3m/s$