Transcript Slide 1

TRANSPORTATION
Energy Use in Cars 3:
Rolling Resistance
Multiple-Choice Questions
Physics and Astronomy Outreach Program at the University of British Columbia
Energy in Cars 3
You are driving across the country and expect to be
going a mostly constant speed. How much fuel do you
save if you travel at 90 km/h rather than 100 km/h?
A.You will burn 5% less fuel
B.You will burn 10% less fuel
C.You will burn 20% less fuel
D.We can’t tell without knowing the car’s CD and Area
E.We can’t tell without knowing the distance traveled.
Physics and Astronomy Outreach Program at the University of British Columbia
Energy in Cars 3
You are driving across the country and expect to be
going a mostly constant speed. How much fuel do you
save if you travel at 90 km/h rather than 100 km/h?
A.You will burn 5% less fuel
B.You will burn 10% less fuel
C.You will burn 20% less fuel
D.We can’t tell without knowing the car’s CD and Area
E.We can’t tell without knowing the distance traveled.
Physics and Astronomy Outreach Program at the University of British Columbia
Energy in Cars 3
The relationship between energy (and hence fuel consumption) and
velocity is:
1
2
KE  AcarCD dv
2
But if all other variables are held the same then:
KE1  v1 
2
KE 2  v 2 
2

where v 2  0.9v1
KE 2 0.9v1

KE1
v12
2
KE 2  .81 KE1  20% fuel is saved
Physics and Astronomy Outreach Program at the University of British Columbia