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4, 000 0.454 9.8
, 700,000 N/m 1 inch
25.4 10 3 m
25.4 10 3
1 lb Question 18 – In the classroom demonstration shown here, a square plate is clamped at its center, and white sand is sprinkled on it. When the plate is made to vibrate, exquisite so‐called Chladni patterns emerge. What is happening? a. friction locally heats up the plate, and the sand collec ts in these warmer areas b. the vibrating plate has nodes and antinodes, and the sand collects in the nodes c. the vibrating plate has nodes and antinodes, and the sand collects in the antinodes d. the vibrations of the plate cause minute air circulatio ns, which blo w the sand over the plate in curly shapes Answer (b) As discussed in class. Vibrational antinodes are locations where there is ma ximum amount of motion; vibrational nodes are the locations where the is no motion. See e.g. Fig. 3.2.7 and surrounding text. PHYS115 – Spring 2013 8 Test 2 - 19 April 2013 Question 19 – If you pull down on the basket of a hanging grocery store scale so that it reads 15 N, how much downward force are you exerting on the basket? a.
d. 15 N more than 15 N less than 15 N more information is needed Answer (a) Equilibrium: force up = force down. Question 20 – When a moving hammer hits a nail, it exerts the enormous force needed to push the nail into wood. This force is far greater than the hammer’s weight. How can this be explained? a.
d. the hammer converts gravitational potential energy into kinetic energy the hammer has a lot of momentum time of conta...
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