Maximum Speed of a Porsche
1. The problem statement, all variables and given/known data
A Porsche 944 Turbo has a rated engine power of 217 hp. 30% of the power is lost in the drive train, and 70% reaches the wheels. The total mass of the car and driver is 1530 kg, and twothirds of the weight is over the drive wheels. What is the speed of the Porsche at maximum power output? 2. Relevant equations P=FV 3. The attempt at a solution I calculated the maximum power by taking 70% of 217 and multiplying by 746W/hp = 113317.4W. I don't know where to go from here, since I'm not sure how to obtain a value for F, the forces doing work on the Porsche at maximum velocity. It's not simply rolling friction, since plugging in (2/3)(1530)(9.8)(.02) (.02 is the value of rolling friction listed in the text) for F yields a maximum speed of 566.8 m/s.... I would think that there would also be a drag force doing work at maximum velocity, but the dimensions of a cross section of the car are not given. Any ideas on how to go about finding vmax? 
Re: Maximum Speed of a Porsche
Well, I found the correct answer....but it doesn't make any sense to me. Using the friction force that accelerates the car as F (2/3)(1530)(9.8)=9996N, I found v to be 11.34m/s. That seems awfully slow for a sports car and for a car at maximum velocity I didn't think that static friction would be doing work.

All times are GMT 5. The time now is 02:11 AM. 
Powered by vBulletin Copyright ©2000  2014, Jelsoft Enterprises Ltd.
© 2014 Physics Forums