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hwk1 solutions

# hwk1 solutions - homework 01 PHAM QUOC Due 1:00 am Question...

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homework 01 – PHAM, QUOC – Due: Jan 22 2008, 1:00 am 1 Question 1, chap 1, sect 4. part 1 of 1 10 points A plastic tube allows a flow of 12 . 7 cm 3 / s of water through it. How long will it take to fill a 249 cm 3 bottle with water? Correct answer: 19 . 6063 s (tolerance ± 1 %). Explanation: Let : r = 12 . 7 cm 3 / s and V = 249 cm 3 . cm 3 ÷ cm 3 s = cm 3 · s cm 3 = s , so the time is defined by t = V r = 249 cm 3 12 . 7 cm 3 / s = 19 . 6063 s . Question 2, chap 1, sect 4. part 1 of 2 10 points The elevators in the John Hancock building in Chicago move 821 ft in 34 s. a) What is their speed in meters per sec- ond? Correct answer: 7 . 36002 m / s (tolerance ± 1 %). Explanation: 1 ft · 12 in . 1 ft · 2 . 54 cm 1 in . · 1 m 100 cm = 0 . 305 m , so v = parenleftbigg 821 ft 34 s parenrightbigg parenleftbigg 0 . 305 m 1 ft parenrightbigg = 7 . 36002 m / s Question 3, chap 1, sect 4. part 2 of 2 10 points b) What is this speed in miles per hour? Correct answer: 16 . 4644 mi / h (tolerance ± 1 %). Explanation: Since 1 mi = 5280 ft and 1 h = 3600 s, v = parenleftbigg 821 ft 34 s parenrightbigg parenleftbigg 3600 s 1 h parenrightbigg parenleftbigg 1 mi 5280 ft parenrightbigg = 16 . 4644 mi / h . Question 4, chap 1, sect 4. part 1 of 3 10 points A hydrogen atom has a diameter of about 9 . 34 nm. a) Express this diameter in meters. Correct answer: 9 . 34 × 10 9 m (tolerance ± 1 %). Explanation: Basic Concept: 1 nm = 1 × 10 9 m 1 μ m = 1 × 10 6 m 1 mm = 1 × 10 3 m Given: diameter = 9 . 34 nm Solution: diameter = 9 . 34 nm = ( 0 . 934 × 10 1 nm ) · 1 × 10 9 m 1 nm = 0 . 934 × 10 8 m Question 5, chap 1, sect 4. part 2 of 3 10 points b) Express this diameter in millimeters. Correct answer: 9 . 34 × 10 6 mm (tolerance ± 1 %). Explanation: Solution: diameter = ( 0 . 934 × 10 8 m ) · 1 mm 1 × 10 3 m = 0 . 934 × 10 5 mm Question 6, chap 1, sect 4. part 3 of 3 10 points c) Express this diameter in micrometers. Correct answer: 0 . 00934 μ m (tolerance ± 1 %). Explanation:

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homework 01 – PHAM, QUOC – Due: Jan 22 2008, 1:00 am 2 Solution: diameter = ( 0 . 934 × 10 8 m ) · 1 μ m 1 × 10 6 m = 0 . 934 × 10 2 μ m Question 7, chap 2, sect 7. part 1 of 1 10 points A sailboat is initially moving at a speed of 2 . 3 m / s. A strong wind blows up and accelerates the boat forward with a constant acceleration of 0 . 3 m / s 2 for 8 s. What is the final speed of the sail boat? Correct answer: 4 . 7 m / s (tolerance ± 1 %). Explanation: The speed of a boat with initial speed v 0 with a constant acceleration a is given by v = v 0 + a t Therefore the speed of the boat after time 8 s s is v = 2 . 3 m / s + (8 s) (0 . 3 m / s 2 ) = 4 . 7 m / s .
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