Question

Anna drives 45 km to work each day.

One day she drives the first 25 km at an average speed of 82 km/h. She takes 36 minutes to drive the remaining distance.
Calculate her average speed, in km/h, for the whole journey.

Answer 1

Anna drove at an average speed of 49.73 km/h

Explanation:

Average Speed

If an object moves at different speeds to cover a certain total distance dt in a total time tt, the average speed is:

`\displaystyle \bar v=(d_t)/(t_t)`

Anna drives a total distance of dt=45 km each day. One day she drives a distance of d1=25 km at v1=82 Km/h. The time taken for that distance is:

`\displaystyle t_1=(d_1)/(v_1)=(25)/(82)=0.3049\ h`

She takes t2=36 minutes to drive the remaining distance. 36 minutes is 36/60=0.6 h, thus the total time is:

`t_t=0.3049\ h+0.6\ h=0.9049\ h`

The average speed is:

`\displaystyle \bar v=(45)/(0.9049)=49.73\ km/h`

Anna drove at an average speed of 49.73 km/h