A runner covers the last straight stretch of a race in 4 s. During that time he speeds up from 5ms to 9ms. What is the unner acceleration in this part of race?

Remember that the average acceleration will the change in velocity per unit time. For a problem like this you merely divide the change in velocity (in meters/sec) by the amount of time (in seconds) to get acceleration in meters per second squared:


Average\ Aceleration\ m/s^2\ = \ \frac {\Delta V\ m/sec} {\Delta T\ sec}


Hope this helps.