An object initially at rest experiences an acceleration of 1.4 m/s^2 for 5.0s and then travels at that constant velocity for another 7.0s. What is the object's average velocity over the 12s interval?

Answer 1

Draw the time-velocity graph.

Initial velocity, u = 0
Acceleration, a = 1.4 m/s²
time, t = 5 seconds
Distance, S1 = ut+(1/2)at²
= 0*5 + (1/2)1.4*5²
= 17.5 m
Final velocity, v = u+at = 0+1.4*5 = 7 m/s
Distance, S2 = 7*7 = 49 m

Average velocity = (S1+S2)/(t1+t2)
=(17.5+49)/(5+7)
= 66.5/12
= 5.54 m/s