Final Exam Review Practice Problems

Transcription

1 Final Exam Review Practice Problems Supplemental Instruction Leader: Matt T Course: Physics 221 Instructor: Whisnant/Ho Date: 5/4/13 Iowa State University 1. Topics: Constant Acceleration, 2-D Motion, Newton s First Law The Stern-Gerlach Experiment: Using Classical Physics to Describe Quantum Effects A very important concept in quantum physics is the intrinsic magnetic dipole built into an electron that basically says an electron creates its own magnetic field (a.k.a force). This can be seen through experiment in which a silver atom is accelerated from an oven (to accelerate the silver atom to a high velocity) and sent through a magnetic field to strike a detector plate. The length of the apparatus is 1 m and the detector is placed flush at the end. The silver atom with mass leaves the oven at perfectly horizontal velocity of = 350 m/s at initial height of y = 0. The force of the magnet acting on the atom in the y-direction ONLY is. Calculate the transverse deflection distance (or the y distance traveled when it hits the detector) of the atom on the detector. Detetector 1 m What collisions of silver atoms like on the detector Supplemental Instruction 1060 Hixson-Lied Student Success Center

2 2. Relative Motion, Center of Mass, Kinetic Energy Consider a two-particle system with one particle at rest at the other with velocity v. Both particles have mass m. Find the kinetic energy of the system from two different perspectives. Find KE 1 from the perspective of a stationary onlooker and KE 2 from the perspective of the center of mass of the system. Before calculating the two, predict whether they should be equal or not. Hints: Define your coordinate axis so the stationary particle has position x = 0. Also, the center of mass will be moving.

3 3. Topics: Thermodynamics, Heat Transfer Recall the difference between thermodynamics and heat transfer: Thermodynamics is concerned with equilibrium states, or states with infinite time ranges, whereas heat transfer considers timerates of energy transfer. For each of the following metals, find the amount of time it will take a 100 kg block to be heated from 300 K to 400 K. For heat transfer, assume a characteristic heat transfer length L of 1 m and a cross-sectional area A of 0.01 m 2. Assume conduction heat transfer. Material Thermal Conductivity, k (W/mK) Specific Heat, C (J/kgK) Density (kg/m 3 ) Beryllium ,850 Copper ,954 Silver ,510 Titanium ,510

4 4. Topics: Root-mean-square Velocity, Escape Velocity, Density A planet is made purely of a single unknown gas. The radius of the planet is 7.70e8 m and the average density of the planet is kg/m 3. From radiation studies, you believe the surface temperature of the planet is approximately 1450K. What chemical species is the planet made of? Recall the volume of a sphere is given by V = 4/3πr 3.

5 5. Topics: Statics: Torque and/or Newton s First Law An outstretched arm has a mass of approximately 4.8 kg and length of 56 cm. Because of the non-uniform muscle distribution, its center of mass is 25 cm from the shoulder. The arm is extended horizontally as the person attempts to hold a 30 pound dumbbell for a few seconds. If the deltoid (shoulder muscle) acts at an angle 12 above the horizontal arm and 12 cm from the shoulder socket, how much tension must the shoulder muscle exert?

6 6. Topics: Radial Acceleration, Gravitation A neutron star is an extremely dense cluster of matter theoretically composed only of dense clusters of neutrons. Their densities are approximately 4e16 kg/m 3. One of the physical difficulties of these stars is that for the stars to not implode upon themselves, the radial acceleration at the surface must equal the gravitational acceleration. If a neutron star was the size of the earth, what would the tangential acceleration that the surface need to be? Recall the radius of the earth is R E = 6.38e6 m and the volume of a sphere is given by V = 4/3πr 3.

7 7. Topics: Sound Waves, Ideal Gas As nervous children in a thunderstorm, we were told to count the time between lightning strikes and we hear thunder and divide that every 5 seconds that passed represented a mile distance between us and the storm. This implies, assuming infinite speed of light, that sound waves travel at a rate of approximately 5 miles per second in air. Using the Ideal Gas Law and the formula for waves propagating in fluids, estimate this number at three different temperatures: 20 C, -30 C, and 50 C. These temperatures correspond to room temperature and very cold and hot days. How valid is this 5 second rule? Is it valid for this metrological range of temperatures? For simplifying purposes, assume air is a diatomic ideal gas with molecular weight M = 29 g/mol and bulk modulus B = 1.42e5 Pa. Also assume a constant atmospheric pressure of 1 bar or 1 atm. There are approximately 1609 m in a mile.

8 8. Topics: Pendulums, Conservation of Mechanical Energy Consider a pendulum of length L that moves a mass m through angle θ. The arm of the pendulum can be considered massless. The maximum height of the mass is h and h < L. Give an expression for the maximum velocity of the mass v in terms of (at most) the following variables: m, g, L, and θ. h