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Unformatted text preview: Le (tl8426) – HW02 – gentle – (56245) 1 This printout should have 31 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. 001 10.0 points Two ants race across a table 56 cm long. One travels at 4 . 4 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: 5 . 09104 cm. Explanation: Let : ℓ = 56 cm , v 1 = 4 . 4 cm / s , and v 2 = 3 . 99999 cm / s . The time it takes the first (faster) ant to cross the finish line is t = ℓ v 1 , and the distance the slower ant covers in that time is s 2 = v 2 t = v 2 ℓ v 1 . The slower ant is ℓ s 2 = ℓ v 2 ℓ v 1 = 56 cm (3 . 99999 cm / s) (56 cm) 4 . 4 cm / s = 5 . 09104 cm from the finish line when the faster one crosses it. 002 (part 1 of 2) 10.0 points You drive a car 9 h at 46 km / h, then 9 h at 65 km / h. What is your average velocity? Correct answer: 55 . 5 km / h. Explanation: Let : t = 9 h , v 1 = 46 km / h , and v 2 = 65 km / h . You drive a distance Δ d = d 1 + d 2 = v 1 t + v 2 t in a time of Δ t = t 1 + t 2 = 2 t , so that the average velocity is v av = Δ d Δ t = v 1 t + v 2 t 2 t = v 1 + v 2 2 = 46 km / h + 65 km / h 2 = 55 . 5 km / h . 003 (part 2 of 2) 10.0 points What is your average velocity if you drive a distance of 499 . 5 km at a speed of 46 km / h, then the same distance at a speed of 65 km / h? Correct answer: 53 . 8739 km / h. Explanation: Let : d = 499 . 5 km , v 1 = 46 km / h , and v 2 = 65 km / h . Δ d = d 1 + d 2 = 2 d and Δ 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)(46 km / h)(65 km / h) 46 km / h + 65 km / h = 53 . 8739 km / h . Le (tl8426) – HW02 – gentle – (56245) 2 004 10.0 points A rocket initially at rest accelerates at a rate of 60 m / s 2 for 0 . 48 min. What is its speed at the end of this time? Correct answer: 1728 m / s. Explanation: Let : a = 60 m / s 2 and t = 0 . 48 min . v f = v o + a t = a t = (60 m / s 2 ) (0 . 48 min) 60 s 1 min = 1728 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 accelerationtime 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. t a 4. t a 5. t a 6. t a 7. None of these graphs is correct. 8. t a correct 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 accelerationtime graph if the car moves toward the right, slowing down at a steady rate?...
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This note was uploaded on 12/05/2011 for the course PHY 301 taught by Professor Swinney during the Fall '07 term at University of Texas.
 Fall '07
 Swinney
 mechanics

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