A train goes from P to Q with a speed u km/h, then from Q to R () with a speed 3u km/h, and returns from R to P with a speed u/2 km/h. What is the average speed (in km/h) of the train for the entire journey starting from P and back to P
Answers
Answer:
average Speed = 2(a+b) ÷ {a/u + b/3u + 2(a+b)/u }
Step-by-step explanation:
Let
the distance from P to Q = a
the distance from Q to R = b
then
the distance from R To P = b
the average Speed = Total distance ÷ total Time
average Speed = 2(a+b) ÷ {a/u + b/3u + 2(a+b)/u }
Answer:18u/23
Step-by-step explanation:
PQ : distance,d = x km ; speed,s = u km/hr ; time, t1 = (distance / speed) = x/u
QR: d = 2x km ; s = 3u km/hr ; t2 = 2x/3u
RP: d= (x+2x=3x km) ; s=u/2 km/hr ; t3= 3x÷(u/2) = 6x/u
Total time = t1+t2+t3
= (x/u)+(2x/3u)+(6x/u)
= 23x/3u
Total distance = PQ+QR+RP
= x+2x+3x
= 6x
Avg speed = total distance / total time
= 6x / (23x/3u)
= 18u/23