The best answer is C. However, a student could make a good case for
answer B. They could say that the engine causes the tires to turn. The
force of the tires on the road causes the reaction force of the road on
the tires which moves the car.
Steven T. Ratliff
Professor of Physics
Northwestern College
3003 Snelling Ave. N.
St. Paul, MN 55113-1598
U. S. A.
Internet: stratliff@nwc.edu
Gary Turner <turner@MORNINGSIDE.EDU>
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02/01/02 05:11 PM
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Subject: Car acceleration
I came across this question in an FCI-type set of questions:
A car accelerates forward from a stop sign. Air resistance slows the
motion. What force causes the car to accelerate forward?
A) It's weight
B) The force of the engine on the tires
C) The friction on the car from the road
D) The upward force exerted on the car by the road
E) The force of the driver on the accelerator pedal
When I first read this, I thought I got the answer (which was the
'correct'
answer). That is below. Then I thought about it some more from an energy
standpoint - now I'm not so sure. What does the group think?