Question

A car moves at `80km` in the first half of total time of motion and at `40km` in the later half. Its average speed is
A. `60km//h`
B. `30km//h`
C. `120km//h`
D. none of these

Answer 1

(a) Average speed `=("Total distance")/("Total time")`
Here, `s_(1)=80xxt/2` and `s_(2)=40xxt/2`
`s_(1)=40 t` and `s_(2)=20t`
Total distance `=s_(1)+s_(2)=40t+20t`
`:.` Total time `=t/2+t/2=t`
`:.` Average speed `=(40t+20t)/t=60km//h`