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  1. J

    Differentiate a thermo equation

    Homework Statement Air at 300K(=T_s) flows over a flat plate maintained at 400K(=T_f). At a particular location on the plate, the temperature distribution in the air measure from the plate surface is given by T(y)=(T_s-T_f)exp[-22,000*y(m)]+T_f Q.Determine the conduction heat flux through...
  2. J

    Work Done in a polytropic process

    Homework Statement A gas is trapped in a cylinder-piston arrangement. The initial pressure and volume are 13,789.5 Pa and 0.02832 m^3. Determine the work(kj) assuming that the volume is increased to 0.08496 m^3 in a polytropic process with n=1. Homework Equations m_1-2=∫PdV from 1 to...
  3. J

    Charge through lightbulb(just needs checked)

    Homework Statement An 80 watt light bulb has a current of .5A running through it. What is the charge through the lightbulb after 1 hour? Homework Equations i=Q/T The Attempt at a Solution For this question is the wattage irrelevant because we know current and time? We would...
  4. J

    Confused about resistance

    Homework Statement A cylindrical copper rod of length L and cross-sectional area A is re-formed to twice its original length with no change in volume. If the resistance between its ends was originally R, what is it now? Homework Equations R=p(L/A) The Attempt at a Solution Using...
  5. J

    Surface area of the earth

    Homework Statement Near Earth, the density of protons in the solar wind (a stream of particles from the Sun) is 8.60 cm-3 and their speed is about 490 km/s. (a) Find the current density of these protons. 6.74E-7 A/m^2 (b) If Earth's magnetic field did not deflect the protons, what total...
  6. J

    Area of parallel plat capacitor

    Homework Statement The plates of a spherical capacitor have radii 31.0 mm and 43.0 mm. What must be the plate area of a parallel-plate capacitor with the same plate separation and capacitance of 12.4pF Homework Equations C=(epsilon*A)/d The Attempt at a Solution...
  7. J

    Surface charge density(error in my work)

    Homework Statement In Figure (a), an electron is shot directly away from a uniformly charged plastic sheet, at a speed of vs = 2.00 106 m/s. The sheet is nonconducting, flat, and very large. Figure (b) gives the electron's vertical velocity component v versus time t until the return to the...
  8. J

    Electron moving between 2 charged plates

    Homework Statement at some instant the velocity components of an electron moving between two charged parallel plates are vx = 1.20 105 m/s and vy = 3.70 103 m/s. Suppose that the electric field between the plates is given by Evec = (120 N/C) jhat. (a) What is the electron's acceleration...
  9. J

    Tension in 2 cables

    Homework Statement A crane is used to lift a concrete pipe weighing 5kN into place. Homework Equations The Attempt at a Solution The picture is in my book, but i am certain my problem is in my algebra(i have the layout correct) T_ac*cos(20)=T_ab*sin(3.58) X direction...
  10. J

    Drawing Free Body Diagrams with torque

    Homework Statement This is a review problem i was given for my final exam tommorow, I am stuck on 1 problem, even with the answer key im not understanding it.(also sorry but the picture wont copy from MSword, but its a cylinder rolling up a hill) (B) When the lander hits the surface, it...
  11. J

    Collision between ball and stick

    Homework Statement On a frictionless table, a 0.58 kg glob of clay strikes a uniform 1.62 kg bar perpendicularly at a point 0.18 m from the center of the bar and sticks to it. If the bar is 0.70 m long and the clay is moving at 6.20 m/s before striking the bar, what is the final speed of the...
  12. J

    Gravitational potential energy of satellite

    Homework Statement A satellite in a circular orbit around the earth with a radius 1.019 times the mean radius of the earth is hit by an incoming meteorite. A large 73-kg fragment is ejected in the backwards direction so that it is stationary with respect to the earth and falls directly to the...
  13. J

    Rotating pendelum

    Homework Statement A uniform stick of length L = 2.2 m, width W = 9.0 cm, and mass M = 4.5 kg oscillates as a physical pendulum and pivots about point O as shown in the Figure. What is the period of the pendulum if x, the distance from the pivot point to the center of gravity of the...
  14. J

    Gravitational force and constants

    Homework Statement Three identical masses of 570 kg each are placed on the x axis. One mass is at x_1 = -10.0 cm, one is at the origin, and one is at x_2 = 43.0 cm. What is the magnitude of the net gravitational force F_grav on the mass at the origin due to the other two masses? Take the...
  15. J

    Disc rolling down hill

    1. The problem statement, all variables and given known data A solid disk of radius 1.60 m and mass 2.30 kg rolls without slipping to the bottom of an inclined plane. If the angular velocity of the disk is 4.9 rad/s at the bottom, what is the height of the inclined plane? Homework...
  16. J

    Two identical, uniform, frictionless spheres

    Homework Statement Two identical, uniform, frictionless spheres, each of weight W , rest in a rigid rectangular container as shown in the figure. Find, in terms of a ratio to W, the forces acting on the spheres due to the container surfaces and one another, if the line of centers of the...
  17. J

    Mass of a rod

    Homework Statement A long thin rod lies along the x-axis from the origin to x=L, with L= 0.750 m. The mass per unit length, l (in kg/m) varies according to the equation l = l0 (1+1.110x2). The value of l0 is 0.500 kg/m and x is in meters. Homework Equations stated in equation The...
  18. J

    Tarzan, angel that rope breaks.

    Homework Statement Tarzan, who weighs 678 N, swings from a cliff at the end of a convenient vine that is 19.0 m long (see the figure). From the top of the cliff to the bottom of the swing, he descends by 3.2 m. If the vine doesn't break, what is the maximum of the tension in the vine...
  19. J

    Work on a box

    Homework Statement A trunk of mass m = 2.3 kg is pushed a distance d = 187 cm up an incline with an angle of inclination q = 18.0° by a constant horizontal force P = 225 N (see figure). The coefficient of kinetic friction between the trunk and the incline is 0.22. Calculate the work done on...
  20. J

    What is the angle theta between vectors

    Homework Statement What is the angle theta between vectors vec A and vec B if vec A = 4 -3 and vec B = -2 + 5? Homework Equations arccos((a dot b)/(|a||b|)) The Attempt at a Solution 4*-2+-3*5=-23 sqrt(4^2+-3^2)*sqrt(-2^2+5^2)=10.39 arc not sure what i am doing wrong but...
  21. J

    Average friction force(energy)

    Homework Statement A 16 g bullet pierces a sand bag 13cm thick. If the initial bullet velocity was 51m/s and it emerged from the sandbag with 14m/s, what is the average magnitude of the friction force the bullet experienced while it traveled through the bag? Homework Equations...
  22. J

    Ski jump-energy

    Homework Statement A skier (m=53.00 kg) starts sliding down from the top of a ski jump with negligible friction and takes off horizontally. If h = 8.00 m and D = 9.50 m, find H. http://img517.imageshack.us/img517/616/prob21a.gif [Broken] Homework Equations .5mv^2+mgh=.5mv^2+mgh The...
  23. J

    Spring question(just need answer checked)

    Homework Statement (a)A spring is attached to a ceiling, and has a relaxed length of 25 cm. When a mass m = 0.80 kg is attached to the spring it stretches to an equilibrium length of L0 = 34 cm. (b) I lift the mass until the spring returns to its relaxed length, and then release it. When...
  24. J

    Tension in2 wires

    Homework Statement Two wires are tied to the 200 g sphere shown in figure. The sphere revolves in a horiIzontal circle at a constant speed of 6.80 m/s. http://img684.imageshack.us/img684/6537/knightfigure0761.jpg [Broken] Homework Equations Ca=m*v^2/r f=ma The Attempt at a...
  25. J

    2 masses 1 on incline

    Homework Statement A mass m2 = 1.1 kg, on a 35.0° incline, is connected to a mass m1 = 6.0 kg, on a horizontal surface. The surfaces and the pulley are frictionless. If F = 17.5 N, what is the magnitude of the tension in the connecting cord...
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