PHYS 217 Exam 2, Fall 2018

Bris; hysics 217 Quiz 2 75 minutes Open book examination Note: Try ONLY three out of the following four questions a. A beam of particles strikes a wall with 2 X 1029 particles per m3 and made up of atoms that behave as perfect spheres of radius r= 4 X 10-15 meters. The particles in the beam have a uniform cross sectional distribution with N particles per unit area. a. What is the total cross section of scattering off an atom of this wall? b. What is the mean free path for scattering within the wall? c. Ifascattered particle in the incoming beam is removed from the beam what thickness of the wall is needed to remove 1/3 the particles in the beam. Consider a person standing at a point on the surface of the earth ata Latitude of 30° from the equator. Using the value of the radius of the earth and its rotational angular velocity, find the velocity of that person as seen in an inertial frame with same center as the earth and fixed relative to the sun. ( take its z-axis as the axis parallel to the axis of rotation of the earth) If this person is running on the surface of the earth towards the north pole at a speed of 2 km/hour. What is his velocity as seen in that same inertial frame? ( define the coordinate system on the surface of the earth to be a natural one with the vertical as the z axis for the frame on that surface and the y axis in the direction towards the north ...the x axis points east) A uniform massive ring of density 5kg/m? and radius r= 20 cm. a. Calculate the principle moments of inertia. b. Ifthe ring is rotating about the axis perpendicular to its plane and going through its center at 500 revolutions per second, what is its angular momentum? What is the kinetic energy of the ring? If the material of the ring is distributed evenly as a disc of the same radius, how would your answers to the parts above change? A disc of mass 2kg and radius 10 cm is hanging from a pivot point 1 cm from and within its circular edge a. Ifitis made to oscillate what is its frequency of oscillations. b. Ifit is released from rest at an angle of 30° from the vertical, what are its angular momentum and its energy? What is the reaction at the pivot when it goes through the mid point of its motion?