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# solution1_pdf - karna(pk4534 HW 5 coker(58245 This...

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karna (pk4534) – HW 5 – coker – (58245) 1 This print-out should have 19 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. 001 10.0 points A hockey puck is given an initial speed oF 30 m / s on a Frozen pond. The puck remains on the ice and slides 111 m beFore coming to rest. The acceleration oF gravity is 9 . 8 m / s 2 . What is the coe±cient oF Friction between the puck and the ice? Correct answer: 0 . 413679. Explanation: Basic Concept: Newton’s Second Law: F net = ma Solution: ²rom kinematics, 0 = v 2 0 + 2 ax a = v 2 0 2 x since the puck comes to a rest. Consider the Free body diagram For the situation: μ N N mg Vertically, the puck is in equilibrium, so F net = N − mg = 0 ⇒ N = mg Horizontally, aFter the puck is given its initial velocity, the Friction Force f k = μ N = μmg is the only unbalanced Force acting on it. Thus, f net = ma = 0 f k = μmg μ = a g = v 2 2 gx = (30 m / s) 2 2(9 . 8 m / s 2 )(111 m) = 0 . 413679 002 10.0 points A block oF mass 5 . 9 kg rests on a plane inclined at an angle oF 26 . The static coe±cient oF Friction between the block and the plane is 0 . 64. What is the Frictional Force on the block? 1. 16 . 2218 N 2. 51 . 9683 N 3. 33 . 2597 N 4. 25 . 3466 N correct 5. 7 . 91307 N Explanation: The maximum static Friction is f max = mgμ cos θ = (5 . 9 kg)(9 . 8 m / s 2 )(0 . 64) cos26 = 33 . 2597 N Since mg sin θ = (5 . 9 kg)(9 . 8 m / s 2 ) sin26 = 25 . 3466 N the Friction is large enough to keep the block From moving, so the static Friction is equal to mg sin θ . 003 (part 1 oF 3) 10.0 points You are driving a car down a straight road at a constant 53 miles per hour. Consider the Following Forces: I) air drag pushing back on the car; II) gravity pulling down on the car; III) the ground pushing up on the car; IV) Friction pushing the wheels (and the car) Forward; and V) Friction pushing the wheels (and the car) back. Which Force(s) act on the car? 1. I, II and III

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karna (pk4534) – HW 5 – coker – (58245) 2 2. II, III and IV 3. I, II, III and IV correct 4. I and II 5. I, III and V Explanation: There are four forces acting on the car. The ground pushing up on the car balances the gravity pushing down in the vertical di- rection; the friction between the wheels and the ground pushing the car forward balances the air drag pushing back on the car. 004 (part 2 of 3) 10.0 points Is there a net or unbalanced force acting on the car? 1. No; the velocity is constant. correct 2. Yes; a net force in the horizontal direc- tion. 3. Cannot be determined 4. No; the speed is constant. 5. Yes; a net force in the vertical direction. Explanation: According to Newton’s Frst law, a moving object will continue moving in a straight line at a constant speed until acted upon by an unbalanced force. The car’s speed is constant and its direction does not change, so there is no net force acting on the car. 005 (part 3 of 3) 10.0 points After a while, the car started to go around a long bend, still maintaining its constant speed of 55 miles per hour.
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solution1_pdf - karna(pk4534 HW 5 coker(58245 This...

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