A brake pad is used to give a normal force of 150N to the outer surface of a 0.25kg spinning disk, in order to slow it down from 250rpm to rest. The disk’s radius is 0.25m. If the coefficient of friction between the pad and the disk is 0.45, how much time was required for the disk to slow from 250 rpm to rest?
A. 0.19s
B. 0.55s
C. 2.4s
D. 12s
D. 12s
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A counterflow double pipe-heat exchanger is used to heat 0.8 kg/s of water from 40ºC to 80ºC with oil having specific heat of 2.1 kJ/kg?K. Assume the maximum oil flow can be 1.0 kg/s and that oil enters the heat exchanger at 170ºC. If the overall heat transfer coefficient is 425 W/m^2?K, determine the surface area of the heat exchanger and the effectiveness of the heat exchanger. Equation 9-29 defines the effectiveness.
What will be an ideal response?
A rocket with a mass of 500 grams is launched straight up. It achieves a velocity of 20.0 m/s in 2.00 seconds. The average thrust force of the engines on the rocket is
A. 7.50 N. B. 9.90 N. C. 12.0 N. D. 13.5 N. E. 20.0 N
In a chiller unit, ammonia is to be condensed at a saturation temperature of 50ºC by passing the ammonia vapor over vertical plates 100 cm high by 150 cm wide and at a surface temperature of 20ºC. Estimate the average convective heat transfer coefficient and the amount of ammonia condensing from one plate surface. Use a value of 1052.8 kJ/kg for hnfg for ammonia.
What will be an ideal response?
In a standing wave, not necessarily at the fundamental frequency, on a string of length L, the distance between nodes is
a. ?/4. b. ?/2. c. ?. d. L/4. e. L/2.