This preview shows pages 1–2. Sign up to view the full content.
2039
. •• (a) Find the electric potential at point P in Figure 20–26. (b) Suppose the three
charges shown in Figure 20–26 are held in place. A fourth charge, with a charge of
+6.11
C
and a mass of 4.71 g, is released from rest at point P. What is the speed of the
fourth charge when it has moved infinitely far away from the other three charges?
Picture the Problem
: The configuration of the three point charges
is shown at the right.
Strategy:
Find the electric potential at point P by summing the
potentials due to the three charges at the vertices of the triangle.
Then multiply the potential by the charge
to determine its
electric potential energy.
Set the potential energy equal to the
kinetic energy to find the speed of the charge when it is infinitely
far away from the other three charges. The distance
between the
point P and the second charge, at the top of the triangle, is
4
q
2
r
2
2
1
2
2
1.25 m
1.25 m
1.08 m.
r
Solution:
1. (a)
Sum the
potentials from each of
the three charges:
2
2
33
12
1
2
123
1
2
3
66
6
9 Nm
C
11
22
2.75 10
C
7.45 10
C
1.72 10
C
8.99 10
76.7 kV
1.25 m
1.08 m
1.25 m
kq
q
kq
kq
q
q
Vk
rrr
r
r
r
2. (b)
Set
and solve for
v
:
ii f
UKUK
f
2
1
4
2
6
4
00
26
.1110 C
2
76,700 V
14.1 m/s
0.00471 kg
qV
mv
q
vV
m
Insight:
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview. Sign up
to
access the rest of the document.
 Fall '06
 Alexandrakis
 Physics, Charge, Electric Potential, Mass

Click to edit the document details