# on18 - 1 Total Points for Problem: 2 Points Solution to...

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Solution for On-Line Homework 18 Motion in a Circle I Solution to On-Line Homework Problem 18.1() Problem: Do objects with uniform circular motion have an accel- eration? Why or why not? Select One of the Following: (a) No, that is why it is called uniform circular mo- tion (b) No, because the velocity stays the same size (c) Yes, because the velocity is changing size. (d-Answer) Yes, because the velocity is changing di- rection. Solution Velocity is a vector quantity, which means it has both mag- nitude and direction. Acceleration is de±ned as the change in velocity, which can mean a change in magnitude, direc- tion, or both. An object in uniform circular motion has a constant speed, i.e. the magnitude of its velocity is constant, but in order for the object to move in a circle, the direction of its velocity is continually changing, which means it has an acceleration. This acceleration is instanta- neously perpendicular to the velocity, so there is no change in the magnitude of the velocity, only in its direction.

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Unformatted text preview: 1 Total Points for Problem: 2 Points Solution to On-Line Homework Problem 18.2(Comparing frictional forces) Problem: How do the coefcients oF Friction between any particular pair oF surFaces compare? Select One oF the ±ollowing: (a) μ k > μ s (b) μ k = μ s (c-Answer) μ k < μ s (d) cannot tell without knowing the types oF sur-Faces involved. Solution The maximum value oF the static Frictional Force occurs the instant beFore the object actually moves (in which case the Friction is then kinetic) when subject to a steadily in-creasing Force. ±or example, suppose a block is sitting on a rough board, and you start trying to move it along the board. You slowly increase the Force you apply to the block. Eventually the Force you apply will be equal in magnitude to the maximum static Frictional Force, F pull = F s = μ s F N IF the pulling Force increases any more, the block will move, and the Friction will then be kinetic. 2 Total Points for Problem: 2 Points 3...
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## This note was uploaded on 05/04/2008 for the course PHYS 2054 taught by Professor Stewart during the Spring '08 term at Arkansas.

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on18 - 1 Total Points for Problem: 2 Points Solution to...

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