Calculate Drag Force for Tennis Ball at 251 km/h

[steve978]

Homework Statement

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.

Homework Equations

Drag Force is: Fd= $\pi$.d².C_D.p_f.u².1/4

The Attempt at a Solution

My attempt is to find Reynolds number: Re_p = (p_fu_td_p)/u = (1.3)(903,600,000)(0.065)/0.000018
and then use a graph of drag coefficient against Re_p 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?

 

[TSny]

Hello steve978.

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