Homework 04

# Homework 04 - Bautista Aldo Homework 4 Due 4:00 am Inst...

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Bautista, Aldo – Homework 4 – Due: Sep 27 2005, 4:00 am – Inst: Maxim Tsoi 1 This print-out should have 28 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 3) 10 points The following 3 questions refer to a towy car which can move to the right or left along a horizontal line (the positive direction along the distance axis is to the right). Assume: Friction is so small that it can be ignored. car v g O + A force is applied to the car. Choose the one force graph for each state- ment below which could allow the described motion of the car to continue. The car moves toward the left with a steady (constant) velocity . 1. t F correct 2. t F 3. t F 4. t F 5. t F 6. t F 7. None of these graphs are correct. 8. t F 9. t F 10. t F Explanation: Since the car moves with constant velocity, there is no force acting on it. t F 002 (part 2 of 3) 10 points

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Bautista, Aldo – Homework 4 – Due: Sep 27 2005, 4:00 am – Inst: Maxim Tsoi 2 The car moves toward the left and is speeding up at a steady rate (constant acceleration ). 1. t F 2. t F 3. t F correct 4. t F 5. t F 6. t F 7. t F 8. t F 9. t F 10. None of these graphs are correct. Explanation: Since the car moves with constant acceler- ation, the force is constance and is negative since the car moves in the negative direction. t F 003 (part 3 of 3) 0 points The car moves toward the left , speeds up, and then slows down. 1. t F 2. t F 3. t F
Bautista, Aldo – Homework 4 – Due: Sep 27 2005, 4:00 am – Inst: Maxim Tsoi 3 4. t F 5. t F correct 6. t F 7. t F 8. t F 9. t F 10. None of these graphs are correct. Explanation: When the car speeds up, the force is in the same direction as the velocity; when it slows down, the force is in the opposite direction. Remember that when the car moves to the left, it is moving in the negative direction. t F 004 (part 1 of 2) 10 points Consider the 696 N weight held by two cables shown below. The left-hand cable had tension 780 N and makes an angle of θ with the wall. The right-hand cable had tension 890 N and makes an angle of θ 1 with the ceiling. 696 N 780 N 890 N θ 1 θ a) What is the angle θ 1 which the right- hand cable makes with respect to the ceiling? Correct answer: 32 . 6353 . Explanation: Observe the free-body diagram below. F 2 F 1 θ 1 θ 2 W g Note: The sum of the x - and y -components of F 1 , F 2 , and W g are equal to zero. Given : W g = 696 N , F 1 = 890 N , θ 1 = 32 . 6353 , and θ 2 = 90 - θ . Basic Concepts: X F x = 0 F x 1 = F x 2 F 1 cos θ 1 = F 2 cos θ 2 (1) F 2 1 cos 2 θ 1 = F 2 2 cos 2 θ 2 (2)

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Bautista, Aldo – Homework 4 – Due: Sep 27 2005, 4:00 am – Inst: Maxim Tsoi 4 and X F y = 0 F y 1 + F y 2 + F y 3 = 0 F 1 sin θ 1 + F 2 sin θ 2 - F 3 = 0 F 1 sin θ 1 = - F 2 sin θ 2 + F 3 F 2 1 sin 2 θ 1 = F 2 2 sin 2 θ 2 - 2 F 2 F 3 sin θ 2 + F 2 3 , since (3) F 3 sin θ 3 = F 3 sin 270 = - F 3 , and F 3 cos θ 3 = F 3 cos 270 = 0 .
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