Question

Alida runs her toy car on dry marble floor, wet marble floor, newspaper and towel spread on the floor. The force of friction acting on the car on different surfaces in increasing order will be
A) Wet marble floor, dry marble floor, newspaper and towel
B) Newspaper, towel, dry marble floor, wet marble floor
C) Towel, newspaper, dry marble floor, wet marble floor
D) Wet marble floor, dry marble floor, towel, newspaper

Answer 1

Hint: Frictional force is greater in rough places. And it is usually lesser in wet surfaces than in dry surfaces. More friction force will be acting on any object if a more rough place or surface is in contact with that object.

Complete step by step answer:
Friction is the force which is generated by the contact of two rough surfaces and opposes the motion. So, it’s obvious that the friction force acting on an object on a more rough place will be greater compared to the friction acting on an object in a less rough place.
Again if the place is wet then there will be a decrease in the contact of rough surfaces which results in the decrease in the friction force.
Since, friction force is directly proportional to the roughness of the contact surface and we know that towel has the most rough surface among all other given objects. So the towel will be last in our answer.
Now, the newspaper is more rough than a dry marble floor surface, so it will have a place before the towel.
Now on comparing wet marble floor and dry marble floor, we already discussed that friction forces will be lesser in wet surfaces rather than in dry surfaces, so wet marble floor will be before dry marble floor.
So our answer comes like this:
Wet marble floor $ < $ Dry marble floor $ < $ Newspaper $ < $ Towel.

Note: Friction force decreases in wet surface compared to dry surfaces because of less interaction between solid – liquid than interaction between solid-solid. And the other useful result is friction force is higher in more rough surfaces compared to less rough surfaces.