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Thermodynamics 650:351 Doyle Knight Department of Mechanical and Aerospace Engineering Rutgers - The State University of New Jersey New Brunswick, NJ USA Tel: 732 445 4464 Email: doyleknight@gmail.com Office hours: Tuesday and Friday, 10:30 am to 12 noon and by appointment Homework Assignment No. 1 Problem 2.34 A steel plate of 950 kg accelerates from rest at 3 m/s2 for a period of 10 s. What force is needed and what is the final velocity ? Solution The force is F = ma = 950 3 = 2, 850 N The final velocity is v = at = 3 10 = 30 m/s 650:351 Thermodynamics Page 1 Homework Assignment No. 1 Problem 2.42 One kilogram of diatomic oxygen (O2, molecular weight 32) is contained in a 500 L tank. Find the specific volume on both a mass and mole basis (v and ). v Solution The specific volume is 500 10-3 volume = = 0.5 m3/kg v= mass 1 The molar specific volume is = v The number of kg-moles in the volume is 1 kg 1 kg-moles = = 32 kg/kg-mole 32 Thus, = v 0.5 = 16 m3/kg-mole 1/32 volume kg-moles 650:351 Thermodynamics Page 2 Homework Assignment No. 1 Problem 2.47 A valve in the cylinder has a cross sectional area of 11 cm2 with a pressure of 735 kPa inside the cylinder and 99 kPa outside. How large a force is needed to open the valve ? Solution The balance forces of on the valve (neglecting the valve weight) is pcylinderA - poutsideA - F = 0 where F is the downwards force required to open the valve. The cross sectional area in m2 is A = 11 10-4 m2 Thus, F = (735 103 - 99 103)(11 10-4) = 699.6 N 650:351 Thermodynamics Page 3 Homework Assignment No. 1 Problem 2.72 A piece of experimental apparatus is located where g = 9.5 m/s2 and the temperature is 5 C. An air flow inside the apparatus is determined by measuring the pressure drop across an orifice with a mercury manometer (see Problem 2.77 for density) showing a height difference of 200 mm. What is the pressure drop in kPa ? Solution The pressure drop is p = mercury g h The density of mercury at 5 C from the equation in Problem 2.77 is 13,582.5 kg/m3. Thus, p = (1.35825 104)(9.5)(0.2) = 25, 810 Pa = 25.8 kPa 650:351 Thermodynamics Page 4 Homework Assignment No. 1 Problem 2.80 The atmosphere becomes colder at higher elevation. As an average the standard atmosphere absolute temperature can be expressed as Tatm = 288 - 6.5 10-3 z where z is the elevation in m. How cold is it outside an airplane cruising at 12,000 m in Kelvin and in Celsius ? Solution By substitution into the equation, T = 210 K = -63.5 C 650:351 Thermodynamics Page 5

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