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HW01 solutions

# HW01 solutions - Kwok(mk2749 HW01 Tsoi(58020 This print-out...

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Kwok (mk2749) – HW01 – Tsoi – (58020) 1 This print-out should have 19 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 (part 1 of 2) 10.0 points The radius of the planet Pluto is 1 . 15 × 10 6 m, and its mass is 1 . 2 × 10 25 kg. Find the average density of Pluto (its mass divided by its volume) if the volume of a sphere is given by 4 3 π r 3 . Correct answer: 1883 . 65 g / cm 3 . Explanation: Let : r = 1 . 15 × 10 6 m = 1 . 15 × 10 8 cm , and m = 1 . 2 × 10 25 kg = 1 . 2 × 10 28 g . Density is ρ = m V = m 4 3 π r 3 = 1 . 2 × 10 28 g 4 3 π (1 . 15 × 10 8 cm) 3 = 1883 . 65 g / cm 3 . 002 (part 2 of 2) 10.0 points Find the surface area of Pluto if the surface area of a sphere is given by 4 π r 2 . Correct answer: 1 . 6619 × 10 13 m 2 . Explanation: Surface area is A = 4 π r 2 = 4 π (1 . 15 × 10 6 m) 2 = 1 . 6619 × 10 13 m 2 . 003 10.0 points A flat circular plate of copper has a radius of 0 . 362 m and a mass of 97 . 4 kg. What is the thickness of the plate? Correct answer: 0 . 0264936 m. Explanation: Let : m = 97 . 4 kg and r = 0 . 362 m . The density of copper is ρ = 8 . 93 × 10 3 kg / m 3 . ρ = m V For a flat circular plate, V = π r 2 h = m ρ h = m ρ ( πr 2 ) = 97 . 4 kg (8930 kg / m 3 ) π (0 . 362 m) 2 = 0 . 0264936 m . 004 (part 1 of 2) 10.0 points A person travels by car from one city to an- other. She drives for 26 . 5 min at 72 . 6 km / h, 9 . 89 min at 93 . 8 km / h, 40 min at 35 . 6 km / h, and spends 13 . 8 min along the way eating lunch and buying gas. Determine the distance between the cities along this route. Correct answer: 71 . 2597 km. Explanation: Distances traveled are x 1 = v 1 t 1 x 2 = v 2 t 2 x 3 = v 3 t 3 Then the total distance traveled is x = x 1 + x 2 + x 3 = (32 . 065 km) + (15 . 4614 km) + (23 . 7333 km) = 71 . 2597 km . 005 (part 2 of 2) 10.0 points Determine the average speed for the trip. Correct answer: 47 . 4064 km / h.

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Kwok (mk2749) – HW01 – Tsoi – (58020) 2 Explanation: And, time spent is t = t 1 + t 2 + t 3 + t other = (26 . 5 min) + (9 . 89 min) + (40 min) + (13 . 8 min) = 1 . 50317 h . Hence v av = x t = 71 . 2597 km 1 . 50317 h = 47 . 4064 km / h . 006 10.0 points A car makes a 229 km trip at an average speed of 41 . 7 km / h. A second car starting 1 h later arrives at their mutual destination at the same time. What was the average speed of the second car for the period that it was in motion? Correct answer: 50 . 984 km / h. Explanation: Basic Concepts: v = Δ x Δ t Solution: The average speed of the second car is given by the distance d divided by the time it takes the second car to travel that distance v 2 = d t 2 . t 2 is given by t 1 , the time it takes the first car to travel the distance d , minus the time difference in which the two cars started t 2 = t 1 t diff . We know that t 1 is given by t 1 = d v 1 , therefore v 2 = d d v 1 t diff . 007 (part 1 of 3) 10.0 points Consider the velocity curve of a one dimen- sional motion along the x -axis. The initial position is x = 10 m. The scale on the horizontal axis is 2 s per division and on the vertical axis 2 m/s per division. a b c time × (2 s) per division velocity × (2 m/s) per division The position at t = 4 s is given by 1. x = 24 m 2. x = 30 m correct 3. x = 10 m 4. x = 18 m 5. x = 28 m 6. x = 22 m 7. x = 20 m 8. x = 16 m 9. x = 12 m 10. x = 14 m Explanation: Change in position is the area under the velocity vs time graph, so x = Δ x + x o
Kwok (mk2749) – HW01 – Tsoi – (58020) 3 = 1 2 (10 m /

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HW01 solutions - Kwok(mk2749 HW01 Tsoi(58020 This print-out...

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