Transcript wk10-ppt
Common Exam 2 results • • • • Graded out of 16 High score for my sections – 18 Low score – 2 Average – 9.15 (about 2.3 points below Exam 1) • HW 9 – due date set incorrectly. Extension for everyone until Saturday 1pm. Iclicker Question #1 Consider the wrench in the figure below. In which direction must a force be applied to the wrench handle at point P to LOOSEN the bolt? A) B) C) D) E) Up Down To the right To the left “If you can do dodge a wrench, you can dodge a ball” P Iclicker Question #1 Consider the wrench in the figure below. In which direction must a force be applied to the wrench handle at point P to LOOSEN the bolt? A) B) C) D) E) “If you can do dodge a wrench , you can dodge a ball” http://www.youtube.com/watch?v=1ZXHsNqkDI4 P Dodgeball (2004) Torque – Or application of force RELATIVE to rotation axis determines direction of rotation Lever arm is reminiscent of a Lever simple machine Location of Force Relative to rotation axis determines direction of rotation Iclicker Question #2 Consider the Atwoods machine below with the pulley having some moment of inertia I (ie. the pulley is no longer massless). Which of the following statements would be true. A) If m1> m2, the masses move as indicated due to the moment of inertia of the pulley. B) It is not possible to choose the masses m1 and m2 so that there is no motion of the masses. C) The magnitude of the accelerations of the masses are not equal. D) The acceleration should depend on the radius of the pulley E) The accelerations of the masses would be larger if the pulley were massless. Iclicker Question #3 Which of the following statements is false concerning a pendulum formed by a mass on the end of a string or one with the mass spread out over a shape of a rigid stick? (Assume Length of string and length of stick the same) A) If the stick and string start from a horizontal position (and at rest) before swinging, the initial potential energy in both cases is the same. B) When both pendulums reach the bottom of the swinging motion, the final potential energy is NOT the same for both cases. C) The moment of inertia for the pendulums are different D) The final angular velocity for both pendulums are the same E) The total mechanical energy for each pendulum is constant. Rolling motion Rolling is combination of pure rotational and pure translational motion Iclicker Question #4 For an object rolling down an incline, which of the following statements is false A) If the object were to SLIDE down the incline (without friction) without rolling, it would reach the bottom faster than it were rolling. B) Energy is not conserved in the process because the friction which causes the object to roll converts some mechanical energy to heat. C) Rolling objects with a larger moment of inertia will have less translational kinetic energy at the bottom of the hill D) Objects with a larger radius do not need to rotate as many times to reach the bottom E) Gravity provides the torque to start the object rolling if it is at rest. Iclicker Question #5 Which of the following statements about angular momentum is false concerning two systems each of which rotates around its center of mass. One is a uniform rod of material. The other is two masses attached to a massless rod. (Assume that both the total mass of each system is the same) A) The angular momentum for both systems is the same if they both rotate at the same angular velocity. B) The angular momentum of the rod would change if it were rotated about its end rather than its middle. C) If both systems were to stop rotating, then the angular momentum for both systems would be zero D) If the angular momentum were constant for both, then they would continue to spin at the same angular frequency. E) A torque directed OUT of the page would be required to DECREASE the angular momentum Do cats always land on their feet? Why do cats always land on their feet? https://www.youtube.com/watch?v=RtWbpyjJqrU Start at 2:14