Spring 2010 - HW03_Solution

# Spring 2010 - HW03_Solution - banuelos(ojb93 – Homework...

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Unformatted text preview: banuelos (ojb93) – Homework 03 – florin – (58140) 1 This print-out should have 12 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points An object is shot vertically upward into the air with a positive initial velocity. What correctly describes the velocity and acceleration of the object at its maximum elevation? Velocity Acceleration 1. positive positive 2. positive negative 3. negative negative 4. zero zero 5. zero negative correct Explanation: At the maximum elevation, the vertical ve- locity is zero. The acceleration is due to gravity, which always acts down. 002 10.0 points A subway train starting from rest leaves a station with a constant acceleration. At the end of 6 . 3 s, it is moving at 13 . 419 m / s. What is the train’s displacement in the first 4 . 8636 s of motion? Correct answer: 25 . 1922 m. Explanation: Let : Δ t = 6 . 3 s , Δ v = 13 . 419 m / s , and t 1 = 4 . 8636 s . a = Δ v Δ t , so the displacement is s = 1 2 a t 2 = 1 2 Δ v Δ t t 2 = 1 2 13 . 419 m / s 6 . 3 s (4 . 8636 s) 2 = 25 . 1922 m . 003 10.0 points The acceleration of gravity is 10 m / s 2 . If there were no air resistance, with what speed would drops hit the Earth if they fell from a cloud 3652 m above the Earth’s sur- face? Correct answer: 270 . 259 m / s. Explanation: Drops would be in free fall and accelerate at 10 m / s 2 . We need to find the time of fall. From d = 1 2 g t 2 , the time is t = radicalBigg 2 d g = radicalBigg 2 (3652 m) 10 m / s 2 = 27 . 0259 s . gain in speed = g t = (10 m / s 2 ) (27 . 0259 s) = 270 . 259 m / s . 004 10.0 points The diagram describes the acceleration vs time behavior for a car moving in the x- direction. b b a P Q t At the point Q , the car is moving 1. with a constant speed. 2. with an increasing speed. correct banuelos (ojb93) – Homework 03 – florin – (58140) 2 3. with a decreasing speed. Explanation: a = d v dt . As long as the acceleration is positive the velocity is always increasing....
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Spring 2010 - HW03_Solution - banuelos(ojb93 – Homework...

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