Physics 115 Test 2 with answers

Question11whileyoureweighingyourselfonabath

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Unformatted text preview: locity, so to the left. PHYS115 - Fall 2012 5/8 Test 2 - November 28, 2012 Question 10 – The cart is pulled to the left, as shown. What frictional force acts on the wheel where it touches the ground (see arrow)? a. b. c. d. static frictional force, to the left static frictional force, to the right sliding frictional force, to the left sliding frictional force, to the right ANSWER: See Fig. 2.2.6 on page 71 in the book, and its discussion. Question 11 – While you’re weighing yourself on a bath room scale, you reach out and push , downward on a nearby table. Is the weight reported by the scale high, low, or correct? a. b. c. d. more information is needed correct low high ANSWER: You push down on table so table pushes up on you. You have zero velocity, so your velocity is constant and your acceleration is zero. Therefore, the head‐to‐tail sum of all forces acting on you must be zero. There are 3 forces: up(from table) + up(from scale) + down(weight); see adjacent diagram. So, force from scale is smaller than weight. force from table weight from scale PHYS115 - Fall 2012 6/8 Test 2 - November 28, 2012 Question 12 – A tennis racket has a sweet spot at its cen ter of percus ssion. If a tennis ball hits this center of percussion, the racket’s handle does not ac celerate. Why? a. the racket’s center of mass accelerates backward while its handle rotates forward about its center of mass and the two motions cancel on e another at the handle b. an impact at the center of percussion exerts no to orque about the racket’s center of mass and doesn’t cause the racket to undergo angular acceleration c. an impact at the center of percussion transfers n o momentum to the racket and doesn’t cause the racket to accelerate d. the racket’s velocity doesn’t change when the ba ll hits its cen of percussion nter ANSWER: See Fig. 3.2.6 on page 107 in the book, and its discussion . Question 13 – You put water in a kitchen blender. After a while, it travels in an 10‐cm radius r circle at a const...
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This document was uploaded on 02/23/2014 for the course PHYSICS 115 at UNL.

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