2012年AP力学简答题真题+答案+PDF下载
Directions: Answer all three questions. The suggested time is about 15 minutes for answering each of the questions,which are worth 15 points each. The parts within a question may not have equal weight. Show all your work in this booklet in the spaces provided after each part.
Mech. 1.
Experiment 1. A block of mass 0.30 kg is placed on a frictionless table and is attached to one end of a horizontal spring of spring constant k, as shown above. The other end of the spring is attached to a fixed wall. The block is set into oscillatory motion by stretching the spring and releasing the block from rest at time t = 0. A motion detector is used to record the position of the block as it oscillates. The resulting graph of velocity u versus time t is shown below. The positive direction for all quantities is to the right.
(a) Determine the equation for v(t) , including numerical values for all constants.
(b) Given that the equilibrium position is at x=0 , determine the equation for x(t), including numerical values for all constants.
(c) Calculate the value of k.
Experiment 2. The block and spring arrangement is now placed on a rough surface, as shown below. The block is displaced so that the spring is compressed a distance d and released from rest.
(d) On the dots below that represent the block, draw and label the forces (not components) that act on the block when the spring is compressed a distance x=d 2 and the block is moving in the direction indicated below each dot.
(e) Draw a sketch of u versus t in this case. Assume that there is a negligible change in the period and that the positive direction is still to the right.
Mech. 2.
You are to perform an experiment investigating the conservation of mechanical energy involving a transformation from initial gravitational potential energy to translational kinetic energy.
(a) You are given the equipment listed below, all the supports required to hold the equipment, and a lab table.On the list below, indicate each piece of equipment you would use by checking the line next to each item.
____ Track ____ Meterstick ____ Set of objects of different masses
____ Cart ____ Electronic balance ____ Lightweight low-friction pulley
____ String ____ Stopwatch
(b) Outline a procedure for performing the experiment. Include a diagram of your experimental setup. Label the equipment in your diagram. Also include a description of the measurements you would make and a symbol for each measurement.
(c) Give a detailed account of the calculations of gravitational potential energy and translational kinetic energy both before and after the transformation, in terms of the quantities measured in part (b).
(d) After your first trial, your calculations show that the energy increased during the experiment. Assuming you made no mathematical errors, give a reasonable explanation for this result.
(e) On all other trials, your calculations show that the energy decreased during the experiment. Assuming you made no mathematical errors, give a reasonable physical explanation for the fact that the average energy you determined decreased. Include references to conservative and nonconservative forces, as appropriate.
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