For the first third of the path, the body moved at a speed of 18 and / s, and the remaining

For the first third of the path, the body moved at a speed of 18 and / s, and the remaining part of the path at a speed of 21 m / s. Find the average speed.

Given:

The traversed path S is divided into two parts 1/3 and 2/3.

the body moved on each section of the path at a different speed:

V1 = 18 m / s at S1 = S / 3;

V2 = 21 m / s at S2 = 2 * S / 3.

Find:

Vav -?

Solution:

To find the average body speed, we apply the formula:

V cp = S / t;

where t = t1 + t2.

t1 = S / 3 * V1;

t2 = 2 * S / 3V2.

We substitute everything in the first formula and we get:

V cf = S / t = S / (t1 + t2) = S / (S / 3 * V1 + 2 * S / 3V2).

It remains to substitute the values into the formula and perform calculations:

V cf = 1 / (1/54 + 2/63) = 19.953 m / s.