1. Jan 2007

3. Power Aims: To know the two ways to calculate power.
To be able consider max speed

4. What is power? Power is the rate of doing work.
The unit of power is the watt (W)
Named after James Watt ( ), Scottish inventor of the steam engine.
1 watt is the power which can produce 1 joule of work every second.
Power = Work Done / Time = Force x distance / Time
Power = Force x velocity

5. What is the power output for the following situations?
A car of mass 900kg moving at a constant speed of 10ms-1 despite a resistance of 300N.
The same car, same speed, same resistance, but travelling up a slope of 100.
The same car on the flat this time with a resistance of 280N, at the instant when its acceleration is 2ms-2 and its velocity is 3ms-1.

9. Answers
Incredible Hulk W Superman 32667W Wonder woman 16000W Batman 12960W Spiderman 7800W Homer 1033W Fred Flintstone 880W Nancy Drew 110W

10. Maximum Velocity Air resistance is proportional to velocity.
An engine can only produce a maximum amount of power then it will reach a top speed.
Velocity
Time

11. Example
A car has mass 1500kg, the engine can produce a maximum power of 80kW. When the car travels at v ms-1, the force of the resistance to motion equal to 25v N.
Find the maximum velocity of the car when travelling:
on horizontal ground.
up a hill with inclination 50.

12. Example
A car has mass 1500kg, the engine can produce a maximum power of 80kW. When the car travels at v ms-1, the force of the resistance to motion equal to 25v N.
Find the maximum velocity of the car when travelling:
on horizontal ground.
up a hill with inclination 50.

13. Questions
Exercise E – page 110
Questions: 6, 7, 8, 9

14. June 2008

16. The 5 Fastest Cars in the World
Bugatti Veyron 16.4 Super Sport
SSC Ultimate Aero TT
SSC Tuatara
Koenigsegg Agera R
9ff Porsche 911 GT2 GTurbo 1200
All data from

17. Air resistance is proportional to velocity squared at high speeds.
Problems to Consider
For each car you have been given:
The top speed
The power
The mass.
Air resistance is proportional to velocity squared at high speeds.
Find out which car is most aerodynamic.
If the cars were to travel up a hill inclined at 50 which car would have the top speed?
When the cars are travelling at 100kmh-1 find the car with the best acceleration.
On flat ground if we increased the weight of the car what would happen to the top speed?
What assumptions are we making for each problem?

18. The Winners
Most Aerodynamic: Bugatti Veyron 16.4 Super Sport Top speed on slope inclined at 50: SSC Tuatara Highest acceleration at 100kmh-1: