The hydrogen-filled airship Hindenburg (see Fig. 11-24) could cruise at 77 knots with the engines providing 4800 hp. Calculate the air drag force in newtons on the airship at this speed.

To obtain air drag force in newtons, substitute 77 knots for v and 4800 hp for P in the equation F = P/v,
F = P/v
= 4800 hp/77 knots
= (4800 hp/77 knots) (745.7 W/1 hp) (1 knot/1.688 ft/s) (1 ft/s/0.3048 m/s)
= 9.0×10⁴ W/m/s
= (9.0×10⁴ W/m/s) (1 N/1 W/m/s)
=9.0×10⁴ N …… (3)
From the above observation we conclude that, air drag force in newtons on the airship at this speed will be 9.0×10⁴ N.