1
(a) The average velocity during any time interval is the displacement during that interval divided
by the duration of the interval:
v
avg
=
∆
x/
∆
t
, where
∆
x
is the displacement and
∆
t
is the time
interval. In this case the interval is divided into two parts. During the first part the displacement
is
∆
x
1
= 40 km and the time interval is
∆
t
1
=
(40 km)
(30 km
/
h)
=1
.
33 h
.
During the second part the displacement is
∆
x
2
= 40 km and the time interval is
∆
t
2
=
(40 km)
(60 km
/
h)
=0
.
67 h
.
Both displacements are in the same direction, so the total displacement is
∆
x
=
∆
x
1
+
∆
x
2
=
40 km + 40 km = 80 km. The total time interval is
∆
t
=
∆
t
1
+
∆
t
2
.
33 h + 0
.
67 h = 2
.
00 h.
The average velocity is
v
avg
=
(80 km)
(2
.
0h)
=40km
/
h
.
(b) The average speed is the total distance traveled divided by the time. In this case the total
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 Spring '07
 KOPP

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