Passage IV

Two types of friction affecting bicycle riders are:

· air resistance

· rolling resistance between the tires and the ground

Table 1 gives the air resistance, RA, affecting a rider moving at speed V when the cross-sectional area of the rider plus bicycle equaled X. Table 1 also gives the power, PA, in watts (W), the rider had to generate to compensate for RA to maintain V. Figure 1 gives the power, PA + R, in horsepower (hp), a rider had to generate to compensate for RA plus rolling resistance to maintain V = 5.6 m/sec or 11. 2 m/sec for a wheel diameter of 16 inches or 27 inches and various tire pressures. Figure 2 is a graph of power in W versus power in hp.

Figure 1 adapted from Frank Roland Whitt and David Gordon Wilson, "Bicycling Science." @1974 by The Massachusetts institute of Technology.

19. According to Figures 1 and 2,for the rider to maintain a V of 11. 2 m/sec on a bicycle with 27 inch wheels and a tire pressure of 80 lb/in2, PA + R, in W, had to be closest to which of the following?

Answer and Explanation

Your Answer is

Correct Answer is C

Explanation

First look at the key in figure 1, find out the curve of V=11.2 m/sec, 27 inches wheel, and then see that when the abscissa tire pressure is 80, the ordinate is about 0.4 hp;

Refer to figure 2, when the abscissa P=0.4, the ordinate power is 300 W