Aparticle that is moving along a straight line accelerates from 40 cm/s to 20 cm/s in 5.0 s and then has a constant acceleration of 20 cm/s^2 during the next 4.0 s. the average speed over the entire time interval is

Average speed,  

Explanation:

Given:

First case

Using equation of motion we have

Now using,

now putting the value of a in first equation we get

Second case

Acceleration

Time taken

using equation of motion in one Dimension we have

Average speed is equal to total distance travelled per unit total time taken

i think it would be 80 km/h because 30 + 50 = 80 (sorry if this not the right answer i'm trying my best)

cant without the picture! ?