Running on a treadmill is slightly easier than running outside because there is
ID: 1323209 • Letter: R
Question
Running on a treadmill is slightly easier than running outside because there is no drag force to work against. Suppose a 60 kg runner completes a 5.0 km race in 15minutes. Part A Determine the drag force on the runner during the race. Suppose that the cross section area of the runner is 0.72 m2 and the density of air is 1.2 kg/m3.Express your answer to two significant figures and include the appropriate units. Part B What is this force as a fraction of the runner's weight?
2.) A 27kg loudspeaker is suspended 2.5m below the ceiling by two cables that are each 60? from vertical. What is the tension in the cables?
Express your answer using two significant figures.
Explanation / Answer
A)
Drag force on the runner is
F = (density ) C A v^2 = ( 1.2 kg/m^3 ) (1) (0.72 m^2 ) (5*10^3 m / 15*60 s) = 4.8 N
B)
F / mg = 4.8 N / ( 60 kg )(9.8 m/s^2 ) = 8.16*10^ -3
2)
horizontal component of tension cancell with each other.
2 T sin 60 = mg
T = (27 kg ) ( 9.8 m/s^2 ) / 2 sin 60 =152.766 N
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