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急！！！physics calc. 20點!!
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求教學~~ Physics Online Homework 急！！！Q1Three people set out from the same location on a Sunday morning for a stroll/joy.John heads north at 9.30 km/h,Sally heads east at 6.90 km/h andJoanna heads south at 4.47 km/h.1a) What is the relative velocity of John as measured by Joanna?__km/h1b) In what... 顯示更多 求教學~~ Physics Online Homework 急！！！ Q1 Three people set out from the same location on a Sunday morning for a stroll/joy. John heads north at 9.30 km/h, Sally heads east at 6.90 km/h and Joanna heads south at 4.47 km/h. 1a) What is the relative velocity of John as measured by Joanna?__km/h 1b) In what direction? West North East South 1c) What is the relative velocity of John as measured by Sally?__km/h 1d)At what angle? (between 0° and 90°, this needs to make sense with the next part) __° 1e) In what direction? Select one: North of west South of east South of west North of east 1f) What is the relative velocity of Sally to Joanna?___km/h 1g)At what angle? (between 0° and 90°)__° 1h) In what direction? South of West North of East North of West South of East Q2 http://postimg.org/image/hnedwnbtt/ 2a)The illustrated pulse travels along the rope towards a metal ring slipped over a pole. It is reflected back along the rope. The rope has a density of 50.0 g/m. The tension in the rope is initially 6287 N. The pulse has a length l = 8.29 cm. The point A on the top is d = 2.61 m from the pole. How long does it take the pulse to travel from point A to the pole and back to A?__s 2b) Which of the following diagrams correctly illustrates the reflected pulse? http://postimg.org/image/q5xrxtob3/ 2c) The tension is increased to 11243 N. What is the length of the pulse now?__cm 更新: 謝謝你~~答案全對呀~~不過還有一題好似遺漏了~~~~~~ 2c) The tension is increased to 11243 N. What is the length of the pulse now?__cm
最佳解答:
1(a) Relative velocity of John measured by Joanna = (9.3 + 4.47) km/h = 13.77 km/h (b) north (c) Relative velocity of John as measured by Sally = square-root[9.3^2 + 6.9^2] km/h = 11.58 km/h (d) Angle = arc-tan(9.3/6.9) degrees = 53.4 degrees (e) north of weat (f) Relative velocity of Sally to Joanna = square-root[6.9^2 + 4.47^2] km/h = 8.22 km/h (g) Angle = arc-tan(4.47/6.9) degrees = 32.94 degrees (h) north of east 2. (a) Speed of pulse = square-root[6287/(50/1000)] m/s = 354.6 m/s Time taken = 2 x 2.61/354.6 s = 0.0147 s (b) option A 2015-01-20 15:18:42 補充： 2(c) By Hooke's Law, tension is proportional to extension of string Hence, new length = 8.29 x (11243/6287) cm = 14.82 cm
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