HW02-solutions

# HW02-solutions - lee (cyl327) HW02 gentle (56245) 1 This...

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Unformatted text preview: lee (cyl327) HW02 gentle (56245) 1 This print-out should have 31 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points Two ants race across a table 68 cm long. One travels at 5 . 01 cm / s and the other at 3 . 99999 cm / s. When the first one crosses the finish line, how far behind is the second one? Correct answer: 13 . 7087 cm. Explanation: Let : = 68 cm , v 1 = 5 . 01 cm / s , and v 2 = 3 . 99999 cm / s . The time it takes the first (faster) ant to cross the finish line is t = v 1 , and the distance the slower ant covers in that time is s 2 = v 2 t = v 2 v 1 . The slower ant is - s 2 = - v 2 v 1 = 68 cm- (3 . 99999 cm / s) (68 cm) 5 . 01 cm / s = 13 . 7087 cm from the finish line when the faster one crosses it. 002 (part 1 of 2) 10.0 points You drive a car 7 h at 47 km / h, then 7 h at 60 km / h. What is your average velocity? Correct answer: 53 . 5 km / h. Explanation: Let : t = 7 h , v 1 = 47 km / h , and v 2 = 60 km / h . You drive a distance d = d 1 + d 2 = v 1 t + v 2 t in a time of t = t 1 + t 2 = 2 t , so that the average velocity is v av = d t = v 1 t + v 2 t 2 t = v 1 + v 2 2 = 47 km / h + 60 km / h 2 = 53 . 5 km / h . 003 (part 2 of 2) 10.0 points What is your average velocity if you drive a distance of 374 . 5 km at a speed of 47 km / h, then the same distance at a speed of 60 km / h? Correct answer: 52 . 7103 km / h. Explanation: Let : d = 374 . 5 km , v 1 = 47 km / h , and v 2 = 60 km / h . d = d 1 + d 2 = 2 d and t = t 1 + t 2 = d v 1 + d v 2 , so that the average velocity will be v av = 2 d d v 1 + d v 2 v 1 v 2 v 1 v 2 = 2 dv 1 v 2 dv 2 + dv 1 = 2 v 1 v 2 v 1 + v 2 = (2)(47 km / h)(60 km / h) 47 km / h + 60 km / h = 52 . 7103 km / h . lee (cyl327) HW02 gentle (56245) 2 004 10.0 points A rocket initially at rest accelerates at a rate of 90 m / s 2 for 0 . 6 min. What is its speed at the end of this time? Correct answer: 3240 m / s. Explanation: Let : a = 90 m / s 2 and t = 0 . 6 min . v f = v o + a t = a t = (90 m / s 2 ) (0 . 6 min) 60 s 1 min = 3240 m / s . 005 (part 1 of 5) 10.0 points Consider a toy car which can move to the right (positive direction) or left on a horizon- tal surface along a straight line. car v O + What is the acceleration-time graph if the car moves toward the right (away from the origin), speeding up at a steady rate? 1. t a 2. t a 3. None of these graphs is correct. 4. t a correct 5. t a 6. t a 7. t a 8. t a Explanation: Since the car speeds up at a steady rate, the acceleration is a constant. 006 (part 2 of 5) 10.0 points What is the acceleration-time graph if the car moves toward the right, slowing down at a steady rate?...
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## This note was uploaded on 02/28/2012 for the course PHY 316 taught by Professor Markert during the Fall '10 term at University of Texas at Austin.

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HW02-solutions - lee (cyl327) HW02 gentle (56245) 1 This...

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