Physics 115 Final With Answers

81 g 15waterleavesthefountaintravelingwithwhatspeed

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Unformatted text preview: 0,000 Pa A: It squirts into the atmosphere, where p = 100,000 Pa. 14. How high can the fountain’s column of water reach? 400,000 4 m 100,000 a. 200,000 20 m 1,000 (9.81) b. c. 300,000 30 m 1,000 (9.81) d. 400,000 40 m 1,000 (9.81) 1 1 A: Bernoulli: p 2 v 2 gh in the reservoir must equal p 2 v 2 gh at the top of the fountain. When the water is still in the reservoir, it is not moving (v=0) and it is at zero height (h=0). 1 So then p 2 v 2 gh p(reservoir) 400,000 At the top of the fountain’s beam of water, the pressure is atmospheric, so p = 100,000, the water isn’t moving either (v=0) and it has some unknown height, we’ll call that unknown height, H. 1 So then p 2 v 2 gh 100,000 gH . We see that 100,000 gH 400,000 which leads to gH 400,000 100,000 300,000 and we find that the unknown height equals H 300,000 300,000 30 m 1000 9.81 g 15. Water leaves the fountain traveling with what speed? PHYS115 – Spring 2012 7 Final Test - 1 May 2012 2 300,000 600 m/s 1,000 a. 300,000 300 m/s 1,000 b. c. 2 300,000 24.5 m/s 1,000 d. 300,000 17.3 m/s 1,000 1 A: Here again we must look at how the value p 2 v 2 gh in the Bernoulli equation changes. 1 Inside the reservoir we have p 2 v 2 gh 400,000 Immediately after the water leaves the 1 1 fountainhead we have p 2 v 2 gh 100,000 2 v 2 with some speed v we must calculate. 1 1 1 We find 400,000 100,000 2 v 2 , so 300 , 000 2 v 2 2 1000 v 2 , and so, finally v2 2 300,000 2 300,000 , and v 1, 000 1, 000 16. You take the elevator from the 3rd floor to the 11th floor Between the 10th and the 11th floor the r. elevator uniformly slows down so it can stop at the 11th floo r. An accelerometer is mounted to the cei‐ ling of the car. Which picture shows the accelerometer betwe en the 10th and the 11th floor? NOTE: Answer (d) is: “cannot tell because the speed is unkno wn”. v (a) v (b) v (c) PHYS115 – Spring 2012 8 Final Test - 1 May 2012 A: The answer is (a). The acceleration points down so th e ‘feeling of acceleration’ in the elevator is up. The accelerom...
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