This particular theoretical question from Friction appeared in IIT JEE 1990 Physics paper. Such questions have often appeared in IIT JEE papers as well as AIEEE papers.

This question enquires of the aspirants a very basic concept. It asks the nature of frictional force exerted on the two wheels of the bicycle by the ground surface. Four options stating the directions are stated and one correct answer must be selected. 

One must keep in mind that while solving questions like this from previous years papers and sample test papers, one must not just memorize the answer and move on to the next question. An important point is to ponder over the concepts underlying it. If you make this simultaneous revision of theoretical concepts a habit, not only would you remember the concepts well, but in the long term your speed would have enhanced a great deal, because you would have such conceptual clarity that the time taken to figure out the procedure would decrease.
These concepts of Mechanics and Newtons Law of Motion are observed in daily lives, and as Friction is not a new concept to the students, its role is also known. From the point of view of IIT JEE papers and AIEEE papers, those questions in which the direction of force of Friction is needed are essentially considered important. Very beautifully with the help of diagrammatic representation the direction on the two wheels has been demonstrated. Diagrams help understand concepts such as this more clearly.
It is known that Friction opposes any kind of relative motion. Therefore if helps the bicycle move in the forward direction. It is a practical observation that in surfaces where there is less friction, i.e. very smooth surfaces, instead of moving forward, the bicycle would skid. Also it is explained in the lecture that it is precisely the frictional force that causes the front wheel of the bicycle to rotate and move forward, because paddling doesn’t move the front wheel as we all know.
So very easily the answer has been obtained which is the very first option, i.e. backward direction on the front wheel, and forward direction on the rear wheel.

 

 

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