A 120-lbm bicyclist is traveling on a level road at 20 miles per hour. What is h

Question

A 120-lbm bicyclist is traveling on a level road at 20 miles per hour. What is her velocity in units of ft/s? What is her kinetic energy in Btu? If the total resistance due to drag and rolling friction is 10 lbf, how much power is she supplying to maintain her speed, in units of hp? If she quit working to maintain speed, how far would she travel before stopping? Assume the drag and rolling friction of 10 lbf remains constant. If instead she is traveling 20 miles/hr and encounters a 10-degree incline, what additional power must she supply to maintain her speed, in units of hp? 29.3ft/s 2.06Btu 0.53hp 160ft 1.11hp

Explanation / Answer

1.

V = speed = 20 miles/hour = 20 (5280 ft/ 1mile) (1 h/3600 sec) = 29.3 ft/s

2.

m = mass = 120 lbm = 54.43 kg

V = speed = 20 miles/hour = 8.94 m/s

Kinetic energy is given as

KE = (0.5) m V2

KE = (0.5) (54.43) (8.94)2 = 2175.12 J = 2175.12 (0.00095 BTU/1J) = 2.06 BTU

c)

F = 10 lbf = 10 (4.45 N/1lbf) = 44.5 N

V = 8.94 m/s

P = F V = 44.5 x 8.94 = 397.83 Watt = 397.83 (1hp /746 Watt) = 0.53 hp

d)

F d = KE

44.5 d = 2175.12

d = 48.87 m = 160 ft

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