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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.