(a) J
(b) J
(c) J2.4 This problem explores the relationship between electric potential energy and work done on a system (by a non-conservative
force) when there is a change in the KE of the system after the work is done. A system consists of a uniform electric field of
73.5 N/C, directed in the positive x direction, together with a particle having a positive charge of 3.46×10í^5 C and a mass of
2.42×10í^9 kg. An external force moves the initially stationary particle from the location x = 3.50 m to the location x = 1.50 m in
the field, and when it stops "pushing" the particle is moving at 346 m/s to the left. (a) What is the change in the kinetic energy
of the system? (b) What is the change in the potential energy of the system? (c) What is the work done on the system by the
external force? (d) Is the change in the potential energy of the system still equal to the work done on the system?
(a) J
(b) J
(c) J
(d) Yes No
2.5 This problem explores the relationship between potential energy and work done by a system (by a conservative force) when
there is a change in the KE of the particle after the work is done. The system consists of a uniform electric field of 42.6 N/C,
directed in the positive x direction, together with a particle with a positive charge of 7.87×10í^6 C. As part of an experiment, the
field is allowed to accelerate the particle starting from rest at x = 1.50 m. The experiment ends when the particle passes
x = 3.50 m, at which time it is moving to the right. (a) What is the change in the kinetic energy of the system? (b) What is the
change in the potential energy of the system? (c) What is the work done by the field on the particle? (d) Is the change in the
potential energy of the system still equal to the negative of the work done by the conservative force?
(a) J
(b) J
(c) J
(d) Yes No
Section 3 - Electric potential energy and work
3.1 Two positive charges of 3.6 μC and 2.5 μC are separated by a distance of 0.031 m. What is the electric potential energy of
this configuration?J3.2 A 6.3 μC point charge and a í1.7 μC point charge are separated by a distance of 0.00032 m. What is the electric potential
energy of this system?
J3.3 The nucleus of a helium atom consists of two protons, each with a charge of +e, and two electrically neutral neutrons. The
distance between the repelling protons is, on the average, about 1×10í^15 m. They are constrained there by a force called,
appropriately enough, the strong force. For each of the following questions, it is sufficient to report your answer with just one
significant digit, multiplied by a power of 10. (a) In a classical, non-quantum model of the helium nucleus, what is the average
strength of the repulsive force between the two protons? (b) What is the average electric potential energy of the nucleus?
(a) N
(b) J3.4 The Bohr model of the hydrogen atom describes it as a proton (charge +e) orbited by a single electron (íe). When the atom
is in its lowest energy state, the orbital radius of the electron is 5.29×10í^11 m, a distance called the Bohr radius. What is the
PEe of a simple system consisting of a proton and an electron separated by that distance?J3.5 The gravitational potential energy of all the water stored behind a very large dam is 1.2×10^16 J, using the base of the dam as
the reference point for zero PE. Imagine you could store the same amount of potential energy in a system consisting of two
particles, each with a charge of 0.0020 C. How far apart should you place the charges?
m3.6 Two small iron spheres each have a charge of 0.250 C. (a) How much work does it take to move the spheres from a
stationary configuration 2.00 m apart to another stationary configuration 1.00 m apart? (b) How much work does it take to
move the spheres from a stationary configuration 12.0 m apart to another stationary configuration 11.0 m apart? (c) How
much work does it take to move the spheres from a stationary configuration 22.0 m apart to another stationary configuration
21.0 m apart?