2.2. Speed and Velocity in One Dimension http://www.ck12.org
Average Velocity
Velocityis different than speed because velocity is a vector quantity and as such will have both a magnitude and a
direction. Velocity is the combination of speed and direction. We define velocity as the change in position divided
by the change in time. Change of position can be either positive or negative, so velocity can be positive or negative.
v=
(Pf−Pi)
(tf−Ti)In the example above, the velocity on the outbound trip is +100 km/hr, while the velocity on the return trip is -100
km/hr (Figure2.7). See below for detailed calculations.
FIGURE 2.7
Velocity vectors on cars indicating direc-
tion and magnitude.Velocity (1):∆∆xt=Pf−Pi=(^100 ( 1 kmhr−− 00 hrkm))= +100 km/hr
Velocity (2):∆∆xt=Pf−Pi=(^0 km( 1 hr−−^10000 hrkm) )=−100 km/hr
Check Your Understanding
- In the example above, the round trip speed and velocity are:
(a) the same
(b) different
Answer:B- The average speed for the entire trip is:
(a) 0 km/hr
(b) 100 km/hr
(c) 200 km/hr
Answer: B. The speed is^2002 hrskm=100 km/hr.- The velocity for the round trip is (Hint, consider the displacement.):
(a) 0 km/hr
(b) +100 km/hr
(c) -200 km/hr
Answer:A. The displacement is zero, therefore^02 kmhrs=0 km/hr.- Construct a table showing the distance, speed, displacement, and velocity over the time intervals [0, 2], [2, 8]
and [8, 10] for Mr. Jones’ travels in the last section.