Question

on the 100 m track , a train travels  the first 30 km at the uniform  speed of 30 km/h. how fast must the train travel the next 70 km so as to average 40km/h for the entire trip?

Answer 1

given d1=30, d2=70. we know that s=d/t and average speed = total distance /total time taken when the train acquired a speed of 30km/h,the time taken is. 30=30/t=30/30. t1=1s. average speed =total distance /total time taken =d1+d2/t1+ t2. t2=time for the second part for 70km. 40=100/1+t2. 40+40t2=100. 40t2=100-40=60. t=1.5h