The rider traveled 8 km / h in the first hour, the next 30 minutes moved 12 km / h, the last 5 km

| September 19, 2021 | education

The rider traveled 8 km / h in the first hour, the next 30 minutes moved 12 km / h, the last 5 km walked at a speed of 5 km / h. Determine the average speed of the rider in the second half of the journey km / h.

t1 = 1 h.

V1 = 8 km / h.

t2 = 30 min = 0.5 h.

V2 = 12 km / h.

S3 = 5 km.

V3 = 5 km / h.

Vср2 -?

To find the average speed of movement in the second half of the path Vav2, it is necessary to divide the length of half of the path S2 “by the time of its movement t2” along the entire path: Vav2 = S2 “/ t2”.

S = S1 + S2 + S3.

S1 = V1 * t1.

S1 = 8 km / h * 1 h = 8 km.

S2 = V2 * t2.

S2 = 12 km / h * 0.5 h = 6 km.

S = 8 km + 6 km + 5 km = 19 km.

S2 “= S / 2 = 19 km / 2 = 9.5 km.

Let’s find the travel time of the second half of the path t2 “: t2” = S3 / V3 + (S2 “- S3) / V2.

t2 “= 5 km / 5 km / h + (9.5 km – 5 km) / 12 km / h = 1.375 h.

Vav2 = 9.5 km / 1.375 h = 6.9 km / h.

Answer: the average speed of the rider in the second half of the journey is Vav2 = 6.9 km / h.



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