Solve 14
explain why it is that one?
Answers
Observation
Let us examine the type of friction occurring in the pictures.
Girl P - Sliding Friction
The girl is dragging the sack. We can observe that there are no rollers nor is the girl rolling the sack to move it.
As the girl tries to move 'slide' the sack, a force of friction acts upon her that resists her motion to slide it. Therefore, we can say that sliding friction is acting upon girl P.
Girl Q - Rolling Friction
This girl here is towing the sack on a trolley. There are rollers attached to the tow.
As the girl tries to move 'roll' the sack, a force of friction resists her motion to roll it. Therefore, we can say that rolling friction is acting upon girl Q.
Which friction is easier to work under?
Rolling friction is easier to work under than sliding friction. This is because during rolling friction, the irregularities of the rollers get relatively less time to interlock with the irregularities of the ground because the object is being rolled and the surfaces have less time to interact. But in sliding friction, irregularities have time to interlock thus making it harder to overcome the friction.
Answer
According to the observations we just made, let us see which of the given statements is/are true.
1. Girl P has to work more against friction.
This statement is correct, as the friction acting upon girl P is harder to overcome than the friction acting upon girl Q.
2. Girl Q does not have to work against friction.
This statement is incorrect. Girl Q does have to work against friction, though relatively less than girl P.
3. The wheels of the trolley have reduced the friction.
This statement is correct. The wheels reduce the friction acting upon girl Q.
Therefore the correct option is (C) 1 and 3 only.