The first 9 km the bus passed at a speed of 36 km / h, and the next 27 km – at a speed of 54 km / h.

The first 9 km the bus passed at a speed of 36 km / h, and the next 27 km – at a speed of 54 km / h. What is the average bus speed?

Given:

S1 = 9 km

V1 = 36 km / h

S2 = 27 km

V2 = 54 km / h

To find:

Vav =?

Decision:

Let’s find the total time and all the way:

Stot = S1 + S2 = 9 km + 27 km = 36 km

T = T1 + T2 = 0.25 h + 0.5 h = 0.75 h,

T1 = S1 / V1 = 9 km / 36 km / h = 0.25 h;

T2 = S2 / V2 = 27 km / 54 km / h = 0.5 h.

Let’s find the average speed over the entire section:

Vav = Stot / T = 36 km / 0.75 h = 48 km / h.

Answer: Vav = 48 km / h.