# HW 4 - Morgan Mena Homework 4 Due Oct 3 2007 11:00 pm Inst...

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Morgan, Mena – Homework 4 – Due: Oct 3 2007, 11:00 pm – Inst: Opyrchal, H 1 This print-out should have 9 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. 001 (part 1 of 1) 10 points An elevator starts from rest with a constant upward acceleration and moves 1 m in the first 1 . 4 s. A passenger in the elevator is holding a 5 . 5 kg bundle at the end of a vertical cord. The acceleration of gravity is 9 . 8 m / s 2 . What is the tension in the cord as the ele- vator accelerates? Correct answer: 59 . 5122 N. Explanation: T mg a elevator g Let h be the distance traveled and a the acceleration of the elevator. With the initial velocity being zero, we simplify the following expression and solve for acceleration of the elevator: h = v 0 t + 1 2 a t 2 = 1 2 a t 2 = a = 2 h t 2 . The equation describing the forces acting on the bundle is F net = m a = T - m g T = m ( g + a ) = m g + 2 h t 2 = (5 . 5 kg) 9 . 8 m / s 2 + 2 (1 m) (1 . 4 s) 2 = 59 . 5122 N . keywords: 002 (part 1 of 1) 10 points Two forces are the only forces acting on a 3 . 1 kg object which moves with an accelera- tion of 2 . 7 m / s 2 in the positive y direction. One of the forces acts in the positive x direc- tion and has a magnitude of 14 N. What is the magnitude of the other force f 2 ? Correct answer: 16 . 3113 N. Explanation: Basic Concepts: X F = m a Solution: f 1 f 2 f ~ f 2 is the hypotenuse of a right triangle, so ~ f 2 = q f 2 + f 1 2 keywords: 003 (part 1 of 1) 10 points

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