For the first 1/4 of the way, the car moved at a speed of 60 km / h

For the first 1/4 of the way, the car moved at a speed of 60 km / h, and the rest of the way – at a speed of 20 km / h. What is the average vehicle speed.

First, let’s write an equation for speed. We already know that speed is the distance divided by the time it took to travel.

v = s0 / (t1 + t2).

And the time that the Car spent on the way is.

t 1 = s1 / v1 = s / 4/60 = s / 240 t2 = s2 / v2 = 3s / 4/20 = 3s / 80.

We already have everything to get the average speed of the car.

v = s / (s / 240 + 3s / 80) = 1 / (1/240 + 9/240) = 1 / (10/240) = 240/10 = 24 (km / h).

So, the average speed of the car along the way: 24 kilometers / hour.