1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    User Avatar
    Homework Helper
    Gold Member
    2017 Award

    Hello steve978.

    Check your conversion of km/h to m/s.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook