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Homework Help: Calculate drag force

  1. Sep 1, 2012 #1
    1. The problem statement, all variables and given/known data

    A tennis player hit a serve of 251 km.h-1 in a match. Calculate the Drag Force acting on the tennis ball. Diameter of ball is 6.5cm, density of air is 1.3 kg.m-3 and air viscosity is 1.8x10-5 kg.m-1.s-1.

    2. Relevant equations

    Drag Force is: Fd= [itex]\pi[/itex].d2.CD.pf.u2.1/4

    3. The attempt at a solution

    My attempt is to find Reynolds number: Rep = (pfutdp)/u = (1.3)(903,600,000)(0.065)/0.000018
    and then use a graph of drag coefficient against Rep to find Cd. However my number for Re is 4.24E+13 which is far too large to be correct. Is there something i am doing wrong?
  2. jcsd
  3. Sep 1, 2012 #2


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    Homework Helper
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    2017 Award

    Hello steve978.

    Check your conversion of km/h to m/s.
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