course Phy 231 Reason out the quantities v0, vf, v, vAve, a, s and t: If an object’s velocity changes at a uniform rate from 10 cm/s to 13 cm/s as it travels 138 cm, then what is the average acceleration of the object?Answer: vf^2 = v0^2 2ads, 2ads = vf^2 – v0^2, a = (vf^2 – v0^2)/(2ds) , ave a = (169cm/s-100cm/s)/(2*138cm) = (69)/(276) = .25cm/s/s. You used and equation rather than reasoning out the result. To reason out the result: Since velocity changes at a uniform rate, you can find the average velocity by averaging initial and final velocities, which you then divide into the displacement to get the time interval. It is very easy to find the change in velocity, which is then divided by the time interval to get the average acceleration. Using the equations which govern uniformly accelerated motion determine vf, v0, a, s and t for an object which accelerates through a distance of 138 cm, starting from velocity 10 cm/s and accelerating at .25 cm/s/s. Answer: vf = 13cm/s, v0 = 10cm/s, ds = 138cm, vAve = (23cm/s)/(2) = 11.5cm/s, dt = ds/vAve = 138cm/11.5cm/s = 12s.