(a) A car travels first `30 km` at a uniform speed of `20 km//h` and next `30 km` at a uniform speed of `40 km//h`. What is its average speed ?
(b) A scooter acquires a speed of `36 km//h` in `10 s`. What is its acceleration?

Explanation

(a) ` t_(1) = ( 30)/( 20) h , t_(2) = ( 30)/( 40) h` , `t = t_(1) + t_(2) = (3)/(2) + (3)/(4) = (9)/(4) h`.
Average speed `= ( s_(1) + s_(2))/(t)= ( 30 + 30)/( 9//4) = 26.7 km//h`
(b) acc. `= ("change in vel.")/("time taken") = ( 36 km//h)/( 10 s) = ( 10 m//s)/(10 s) = 1 m//s^(2)`