Answer:
Suppose at time t1 = zero and v1 = 50 MPH
time t2 = 10 sec and v2 = 10 MPH
Change in speed = (v2 - v1) / (t2 - t1) = (10 - 50) MPH / (10 - 0) sec
Change in speed = -40 MPH / 10 sec = - 4 MPH / sec
If you specify the velocity as always East then
change in velocity = - 4 MPH East
Had the particle finished by moving in the Westerly direction then
Change in velocity = (-10 - 50) MPH / 10 sec = -60 / 10 MPH = -60 MPH East
Where West was the positive direction
Initially v1 was 50 East and v2 was -10 East with a difference of 60 MPH
