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**Unformatted text preview: **PHYS115 – Spring 2012 1 Final Test - 1 May 2012 g = 9.81 m/s2, Boltzmann constant = 1.38 x 10−23 J/K
1 inch = 25.4 mm , 1 pound = 1 lb = 0.454 kg , 1 pound‐force = 1 lbf = 1 lb × g mass density of air = 1.26 kg/m3 , mass density of water = 1,000 kg /m3 , mass density of mercury = 13,600 kg/m3 pressure of the atmosphere = 100,000 Pa 1. A: momentum = mass x speed so if speed is constant, momentum won’t change speed constant means acceleration is zero Newton’s 2nd Law: force = mass x acceleration = mas s x 0 = 0 2. 1
A: kinetic energy = mass x speed2 (in symbols Ekin 2 m v 2 ) so if speed doubles (2x), kinetic energy quadruples (4x) PHYS115 – Spring 2012 2 Final Test - 1 May 2012 3. A: Bernoulli: p 1 v 2 gh must be the same everywhe re 2
bottom of straw: p 1 v 2 gh p(atmosphere) 1 0 2 g 0 p(atmo sphere) 2
2
top of column of water (where there’s vacuum so p=0): p 1 v 2 gh 0 1 0 2 gh gh
2
2
so gh p(atmosphere) and this means h p(atmosphere)
g Height is limited by how big the atmospheric pressure is
s. 4. A: buoyant force is up, and equals weight of fluid displa ced weight of object is down because object sinks, net force is down, so weight is bigg er than weight of fluid displaced 5. How much force is the atmospheric air exerting on the fro nt surface of a book with dimensions 21 × 33 cm? a. 6930 N b. 69.3 × 106 N PHYS115 – Spring 2012 3 Final Test - 1 May 2012 c. 6930 Pa/m2 d. 100,000 Pa/m2 A: force = area x pressure area = 0.21 x 0.33 = 0.0693 m2 pressure = 100,000 Pa force = 0.0693 x 100,000 = 6930 N 6. Water weighs about 10 N per liter on Earth. A 3.0 liter ball is pushed underwater on board of the space shuttle, where gravity was 1/10 that on Earth. What is the buoyant force on the ball? a. 1 N b. 10 N c. 3 N d. 30 N A: Volume is 3 L. Buoyant force = weight (in shuttle) of 3 L of water. ed
Water has a mass density of 1,000 kg/m3, so the mass of the 3 L of water displace is –3 x 1000 = 3 kg. In the shuttle, this has a w eight of mass = 3x10
mass x g(shuttl...

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