A 50.0-kg box is being pulled along a horizontal surface by means of a rope that exerts a force of 250 N at an angle of 32.0° above the horizontal. The coefficient of kinetic friction between the box and the surface is 0.350
What is the acceleration of the box? A) 0.638 m/s2
B) 1.74 m/s2
C) 3.16 m/s2
D) 6.31 m/s2
E) 8.53 m/s2
B
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A clown at the circus blows up a balloon with helium. This balloon will not float to the ceiling unless
A. the pressure of the helium inside the balloon is less than the atmospheric pressure. B. the balloon and the helium it contains weigh less than the air displaced by the balloon. C. the pressure of the helium inside the balloon is greater than the atmospheric pressure. D. the weight of the balloon is less than the weight of the air displaced by the balloon.
Hot water is used to heat air in a double pipe heat exchanger as shown in the following sketch. If the heat transfer coefficients on the water side and on the air side are 550 W/(m2K) and 55 W/(m2 K), respectively, calculate the overall heat transfer coefficient based on the outer diameter. The heat exchanger pipe is 5 cm, schedule 40 steel (k = 54 W/m K), with water inside but assume that a fouling factor of 0.173 (m2 K ) /kW based on the tube outside diameter has developed over time.
GIVEN • A double pipe heat exchanger with water in inner tube and air in the annulus • Heat transfer coefficients ? Water side h i= 550 W/(m2 K) ? Air side h o= 55 W/(m2 K) • Inner pipe: 2 in., schedule 40, made of steel • Pipe thermal conductivity (k) = 54 W/(m K) • Fouling factor (Rd) = 0.173 (m2 K )/kW= 1.73*10-4 (m2 K )/kW, based on the tube outside area FIND • The overall heat transfer coefficient based on the outer diameter (Uo) ASSUMPTIONS • Uniform heat transfer coefficients • The given fouling factor is based on the outer tube diameter (Do)
Suppose an average molecule's displacement is 1.2 m in one hour. What is the diffusion constant in SI units (m, kg, s)
a. 4.0 × 10^-4 SI units c. 2.8 × 10^-5 SI units b. 1.0 × 10^-4 SI units d. 4.6 × 10^-8 SI units
A star has a parallax of 0.04 arc seconds. What is its distance?
A. 25 light-years B. 4 parsecs C. 4 light-years D. 25 parsecs