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 3
Question / Topic / Problem1 / Section 10.1 Angular Position, Velocity, and Acceleration / No 2 (Softcopy) p.308; No 2 (Hardcopy) p. 308
2. A potter’s wheel moves uniformly from rest to an angular
speed of 1.00 rev/s in 30.0 s. (a) Find its average angular
acceleration in radians per second per second. (b) Would
doubling the angular acceleration during the given period
have doubled the final angular speed?
2 / Section 10.2 Analysis Model: Rigid Object Under Constant Angular Acceleration / No 8 (Softcopy) p.308; No 6 (Hardcopy) p. 308
8. A machine part rotates at an angular speed of
0.060 rad/s; its speed is then increased to 2.2 rad/s at an
angular acceleration of 0.70 rad/s2. (a) Find the angle
through which the part rotates before reaching this final
speed. (b) If both the initial and final angular speeds are
doubled and the angular acceleration remains the same,
by what factor is the angular displacement changed? Why?
3 / Section 10.7 Analysis Model: Rigid Object Under a Net Torque / No 38 (Softcopy) p.311; No 38 (Hardcopy) p. 311
38. A grinding wheel is in the form of a uniform solid disk of
radius 7.00 cm and mass 2.00 kg. It starts from rest and
accelerates uniformly under the action of the constant
torque of 0.600 Nm that the motor exerts on the wheel.
(a) How long does the wheel take to reach its final operating
speed of 1 200 rev/min? (b) Through how many revolutions
does it turn while accelerating?
4 / Section 12.3 Examples of Rigid Objects in Static Equilibrium / No 18 (Softcopy) p.366; No 18 (Hardcopy) p. 366
18. A 20.0-kg floodlight in a park is supported at the end of a horizontal beam of negligible mass that is hinged to a pole as shown in Figure P12.18. A cable at an angle of = 30.0with the beam helps support the light. (a) Draw a force diagram for the beam. By computing torques about an axis at the hinge at the left-hand
end of the beam, find (b) the tension in the cable, (c) the horizontal component of the force exerted by the pole on the beam, and (d) the vertical component of this force. Now solve the same problem from the force diagram from part (a) by computing torques around
the junction between the cable and the beam at the righthand
end of the beam. Find (e) the vertical component of the force exerted by the pole on the beam, (f) the tension in the cable, and (g) the horizontal component of the force exerted by the pole on the beam. (h) Compare the solution to parts (b) through (d) with the solution to parts (e) through (g). Is either solution more accurate?
5 / Section 12.4 Elastic Properties of Solids / No 27 (Softcopy) p.368; No 29 (Hardcopy) p. 368
27. A 200-kg load is hung on a wire of length 4.00 m, cross-sectional area 0.200 104m2, and Young’s modulus
8.00 1010N/m2. What is its increase in length?
6 / Additional Problems / No 39 (Softcopy) p.369; No 39 (Hardcopy) p. 369
39. In exercise physiology studies, it is sometimes important to
determine the location of a person’s center of mass. This
determination can be done with the arrangement shown
in Figure P12.39. A light plank rests on two scales, which
read Fg1 = 380 N and Fg2 = 320 N. A distance of 1.65 m
separates the scales. How far from the woman’s feet is her
center of mass?
7 / Section 15.2 Analysis Model: Particle in Simple Harmonic Motion / No 15 (Softcopy) p.458; No 15 (Hardcopy) p. 458
15. A 0.500-kg object attached to a spring with a force constant
of 8.00 N/m vibrates in simple harmonic motion with an
amplitude of 10.0 cm. Calculate the maximum value of its
(a) speed and (b) acceleration, (c) the speed and (d) the
acceleration when the object is 6.00 cm from the equilibrium
position, and (e) the time interval required for the
object to move from x = 0 to x = 8.00 cm.
8 / Section 15.3 Energy of the Simple Harmonic Oscillator / No 21 (Softcopy) p.458; No 23 (Hardcopy) p. 458
21. A simple harmonic oscillator of amplitude A has
a total energy E. Determine (a) the kinetic energy and
(b) the potential energy when the position is one-third
the amplitude. (c) For what values of the position does the
kinetic energy equal one-half the potential energy? (d) Are
there any values of the position where the kinetic energy is
greater than the maximum potential energy? Explain.
9 / Section 15.5 The Pendulum / No 26 (Softcopy) p.459; No 26 (Hardcopy) p. 459
26. A “seconds pendulum” is one that moves through its equilibrium position once each second. (The period of the pendulum is precisely 2 s.) The length of a seconds pendulum
is 0.992 7 m at Tokyo, Japan, and 0.994 2 m at Cambridge,
England. What is the ratio of the free-fall accelerations at
these two locations?
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