Find the average speed if the body moved 2 kilometers at a speed of 72 km / h

Find the average speed if the body moved 2 kilometers at a speed of 72 km / h, and the next section of 500 m it passed in 3 minutes.

S1 = 2 km = 2000 m.

V1 = 72 km / h = 20 m / s.

S2 = 500 m.

t2 = 3 min = 180 s.

Vav -?

To find the average speed of movement of the body Vav, it is necessary to divide the entire path S it has traveled by the time of its passage t: Vav = S / t.

We express the entire path S of movement by the sum: S = S1 + S2.

S = 2000 m + 500 m = 2500 m.

The travel time of the entire path is expressed by the sum: t = t1 + t2, where t1 is the time of movement on the first part of the path, t2 is the time of movement on the second part of the path.

Since the body moved uniformly in the sections, we will express the time of passage of the first section t1 by the formula: t1 = S1 / V1.

t1 = 2000 m / 20 m / s = 100 s.

t = 100 s + 180 s = 280 s.

Vav = 2500 m / 280 s = 8.9 m / s = 8.9 * 3600 km / 1000 h = 32 km / h.

Answer: the average speed of body movement is Vav = 8.9 m / s = 32 km / h.