advertisement

UiTM – Faculty of Applied Science Test 3 – Set B - PHY430 – AS2232/CS2273 – 21.6.12 SOLUTIONS Answer all the questions (g = 9.80 m/s2) 1. a) State and explain Continuity Equation. Continuity Equation: A1v1 = A2v2 = constant The product of the area and the fluid speed at all points along a pipe is constant for an incompressible fluid. Volume : symbol capital V speed: symbol small v ๐๐ The product Av is called the volume flow rate ( ) which has the dimension of ๐๐ก volume per unit time. b) Water flowing through a garden hose of diameter 0.030 m fills a 0.025-m3 bucket in 90 s. Determine i) the rate at which the water fills the bucket ๐๐ ๐๐ก = 0.025 90 ๐3 = 2.8 × 10−4 ๐ ii) the speed of the water leaving the end of the hose ๐ด1 ๐ฃ1 = ๐ฃ1 = ๐๐ ๐๐ก 2.8 × 10−4 0.030 2 ๐( ) 2 = 0.40 ๐ ๐ iii) the speed of the water leaving the end of the hose if the cross-sectional area of the end of the hose is reduced to one-third its original cross-sectional area. ๐ด2 ๐ฃ2 = ๐ฃ2 = ๐๐ ๐๐ก 2.8 × 10−4 1 0.030 2 ( )๐( ) 3 2 = 1.2 ๐ ๐ 2. A sinusoidal travelling wave on a string is represented by y = 0.15 sin (0.80x + 50t) where y and x are in meters and t is in seconds. For this wave determine Compare y = 0.15 sin (0.80x + 50t) y = A sin (kx + ๏ทt) k = 0.80 m๏ญ1 and ๏ท = 50 rad/s a) the wavelength ๐= 2๐ 2๐ 2๐ โน๐= = = 7.9 ๐ ๐ ๐ 0.80 b) frequency ๐ = 2๐๐ โน ๐ = ๏ท 50 = = 8.0 ๐ −1 2๏ฐ 2๏ฐ c) velocity of the wave (magnitude and direction) ๐ฃ = ๐๐ = (7.9)(8.0) = 63 ๐ ๐ก๐ ๐กโ๐ ๐๐๐๐ก ๐ d) maximum and minimum speed of the particles of the string. ๐ฃ๐๐๐๐ก๐๐๐๐ = ๐๐ฆ = 0.15 ๐๐๐ (0.80๐ฅ + 50๐ก)(50) ๐๐ก = 7.5 ๐๐๐ (0.80๐ฅ + 50๐ก) ๐ฃ๐๐๐๐ก๐๐๐๐ ๐๐๐๐๐๐ข๐ = 0 ๐คโ๐๐ ๐๐๐ (0.80๐ฅ + 50๐ก) = 0 ๐ ๐ฃ๐๐๐๐ก๐๐๐๐ ๐๐๐ฅ๐๐๐ข๐ = 7.5 ๐คโ๐๐ ๐๐๐ (0.80๐ฅ + 50๐ก) = 1 ๐ 3. a) State the meaning of i) specific heat capacity Heat needed to increase the temperature of a 1 kg substance by 1 K. ๐ฝ The unit is ๐๐โ๐พ. ii) latent heat of vaporization. Heat needed to change a 1 kg substance from liquid to gas without any temperature change. The unit is ๐ฝ . ๐๐ b) Calculate the amount of thermal energy needed to change a 0.720-kg ice at ๏ญ10๏ฐC to water at 15๏ฐC. Q needed = Q to increase the temperature of ice from ๏ญ10๏ฐC to 0๏ฐC + Q to melt all the ice at 0๏ฐC + Q to increase the temperature of water from 0๏ฐC to 15๏ฐC = mi ci ๏๏ฑi + mi Lf + mw cw ๏๏ฑw = (0.720)(2100)(0 ๏ญ ๏ญ10) + (0.720)( 3.33 ๏ด 105) + (0.720)(4200)(15 ๏ญ 0) = 3.00 ๏ด 105 J Specific heat of ice = 2100 J/kg.K Specific heat of water = 4200 J/kg.K Latent heat of fusion of water = 3.33 ๏ด 105 J/kg