A remote control electric toy car of mass 0.5kg starts from rest and reaches a speed of 1.8m/s in 2s while travelling south along a straight level path. During this time the average force needed to overcome friction is 0.25N.
What force is exerted by the motor of the car during this time? (Assume that this force is constant.)
The Attempt at a Solution
The observed acceleration is .9m/s^2 hence an observed force of .45N forwards. The car in travelling must also provide a .25N in the same direction in order to eliminate friction so that comes to a total of .7N exerted by the motor. Correct?
The answer at the back of the book suggested .45N only. Is the answer wrong?