ch4 continued pt2

ch4 continued pt2 - Announcements Submission deadline for...

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Announcements Submission deadline for Homework 3 (Ch. 4 and 5) extended to Wednesday, Sept. 30 th @ 8am . Homework 4 (Ch. 6) is still due Friday, Oct. 2 nd @ 8am. TA recitation: HSS 2.01.36 Friday 3:00- 4:00pm 1
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Chapter 4 The Laws of Motion ontinued continued 2
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Problem 4.78 A sled weighing 60.0 N is pulled horizontally across snow so that the coefficient of kinetic friction between sled and snow is 0.100. A penguin weighing 70.0 N pg g g rides on the sled. If the coefficient of static friction etween penguin and sled is between penguin and sled is 0.700, find the maximum horizontal force that can be xerted on the sled before exerted on the sled before the penguin begins to slide off. 3
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Block on a Ramp, Example Axes are rotated as usual on an incline Direction of impending motion would be down the plane so friction acts up the plane pply ewton’s Laws Apply Newton s Laws and solve equations 4
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Problem 4.53 Find the acceleration reached by each of the two objects shown if the coefficient of kinetic friction between the 7.00 kg object and the lane is 0 250 plane is 0.250. 5
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Connected Objects Apply Newton’s Laws separately to each bject T ± x object The magnitude of the acceleration of both T n 12.0 kg 7.00 kg ± y objects will be the same he nsion the w ² 118 N w ² 68.6 N f 37.0 ° The tension is the same in each diagram Solve the simultaneous equations 6
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Other Types of Friction Friction - resistance encountered y an object moving on a surface riction between the by an object moving on a surface or through a viscous medium. Friction between the moving car’s wheels and the road is static friction Also have drag or air resistance, , R 7
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Chapter 5 Energy 8
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Forms of Energy Mechanical Kinetic - associated with motion Potential - associated with position Chemical – batteries Electromagnetic – sound, light uclear Nuclear 9
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Some Energy Considerations Energy can be transformed from one form to another The total amount of energy in the Universe never changes Can be used in place of Newton’s laws to solve certain problems more simply 10
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Physics definition of work volves applying a force to an object Involves applying a force to an object while moving it a given distance 11
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Work General W = (F cos ) x F is the magnitude of the force Δ x is the agnitude of the magnitude of the object’s displacement is the angle between nd x and Fx 12
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Work, cont. Work gives no information about The time it took for the displacement to occur The velocity of the object The acceleration of the object Work is a scalar quantity SI units – Joule (J = kg • m 2 / s 2) J = N • m US Customary - ft • lb 13
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Summary on work Force and cos WE x a m ple W = (F cos ) x displacement parallel cos 0°=1 positive perpendicular cos 90°=0 zero antiparallel cos 180°=-1 negative 14
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Examples a) b) c) 15
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Summary on work Force and cos WE x a m ple W = (F cos ) x displacement parallel cos 0°=1 positive perpendicular cos 90°=0 zero antiparallel cos 180°=-1 negative 16
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ch4 continued pt2 - Announcements Submission deadline for...

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