Download PHY440 - Assignment 2 - 25.9.13

PHY440 Mechanics, Waves and Thermal Physics
Text book: Jewett, J.W. and Serway, R.A. (2010). Physics for Scientists and Engineers with Modern
Physics, 8th Edition, Brooks/Cole Cengage Learning.
Assignment 2
Question
1
Topic
Sections 5.1 through 5.6
The Laws of Motion
Problem
No 11 (Softcopy) p.131; No 9 (Hardcopy) p. 131
11. An object of mass m is dropped at t = 0 from the roof
of a building of height h. While the object is falling, a wind
blowing parallel to the face of the building exerts a constant
horizontal force F on the object. (a) At what time t
does the object strike the ground? Express t in terms of
g and h. (b) Find an expression in terms of m and F for
the acceleration ax of the object in the horizontal direction
(taken as the positive x direction). (c) How far is the object
displaced horizontally before hitting the ground? Answer
in terms of m, g, F, and h. (d) Find the magnitude of the
object’s acceleration while it is falling, using the variables
F, m, and g.
2
3
Section 5.7 Some
Applications of Newton’s
Laws
No 30 (Softcopy) p.133; No 30 (Hardcopy) p. 133
Section 5.8 Forces of
Friction
No 39 (Softcopy) p.134; No 37 (Hardcopy) p. 134
30. Two objects are connected by a light string that passes over a
frictionless pulley as shown in Figure P5.30. Assume the incline is
frictionless and take m1 = 2.00 kg, m2 = 6.00 kg, and  = 55.0°. (a)
Draw free-body diagrams of both objects. Find
(b) the magnitude of the acceleration of the objects, (c) the tension
in the string, and (d) the speed of each object 2.00 s after it is
released from rest.
39. A 25.0-kg block is initially at rest on a horizontal surface.
A horizontal force of 75.0 N is required to set the block in
motion, after which a horizontal force of 60.0 N is required
to keep the block moving with constant speed. Find (a) the
coefficient of static friction and (b) the coefficient of
kinetic friction between the block and the surface.
4
Section 7.4 Work Done by a
Varying Force
No 24 (Softcopy) p.194; No 26 (Hardcopy) p. 194
24. The force acting on a particle is Fx = (8x + 16), where F is
in newtons and x is in meters. (a) Make a plot of this force
versus x from x = 0 to x = 3.00 m. (b) From your graph,
find the net work done by this force on the particle as it
moves from x = 0 to x = 3.00 m.
5
6
Section 7.5 Kinetic Energy
and the Work–Kinetic
Energy Theorem
No 36 (Softcopy) p.195; No 36 (Hardcopy) p. 195
Additional Problems
No 55 (Softcopy) p.196; No 55 (Hardcopy) p. 196
36. Review. In an electron microscope, there is an electron
gun that contains two charged metallic plates 2.80 cm
apart. An electric force accelerates each electron in the
beam from rest to 9.60% of the speed of light over this distance.
(a) Determine the kinetic energy of the electron as
it leaves the electron gun. Electrons carry this energy to
a phosphorescent viewing screen where the microscope’s
image is formed, making it glow. For an electron passing
between the plates in the electron gun, determine (b) the
magnitude of the constant electric force acting on the electron,
(c) the acceleration of the electron, and (d) the time
interval the electron spends between the plates.
55. Review. A baseball outfielder throws a 0.150-kg baseball
at a speed of 40.0 m/s and an initial angle of 30.0 to the
horizontal. What is the kinetic energy of the baseball at the
highest point of its trajectory?
7
8
9
Section 8.3 Situations
Involving
Kinetic Friction
No 14 (Softcopy) p.225; No 16 (Hardcopy) p. 225
Chapter 9 Linear
Momentum and Collisions
No 53 (Softcopy) p.273; No 53 (Hardcopy) p. 273
Chapter 9 Linear
Momentum and Collisions
No 65 (Softcopy) p.274; No 65 (Hardcopy) p. 274
14. A 40.0-kg box initially at rest is pushed 5.00 m along a
rough, horizontal floor with a constant applied horizontal
force of 130 N. The coefficient of friction between box and
floor is 0.300. Find (a) the work done by the applied force,
(b) the increase in internal energy in the box–floor system
as a result of friction, (c) the work done by the normal
force, (d) the work done by the gravitational force, (e) the
change in kinetic energy of the box, and (f) the final speed
of the box.
53. A ball of mass m is thrown straight up into the air with
an initial speed vi. Find the momentum of the ball (a) at its
maximum height and (b) halfway to its maximum height.
65. Review. A bullet of mass m is fired into a block of mass
M initially at rest at the edge of a frictionless table of height
h (Fig. P9.65). The bullet remains in the block, and after impact the
block lands a distance d from the bottom of the
table. Determine the initial speed of the bullet.