Friction - Exemplar Solutions 4
NCERT Exemplar Solutions
CHAPTER – 12
Friction
LONG ANSWER QUESTIONS
22. When the cutting edge of a knife is put against a fast-rotating stone to sharpen it, sparks are seen to fly. Explain the reason.
Ans: Friction generates heat. When the cutting edge of a knife comes in contact with a fast-rotating stone, heat is produced due to friction between the grinding stone and the cutting edge of the knife. As the friction is very large, a large amount of heat is produced and sparks are seen flying while sharpening the cutting edge of the knife.
23. We have two identical metal sheets. One of them is rubbed with sand paper and the other with ordinary paper. The one rubbed with sand paper shines more than the other. Give reason.
Ans: The friction between the sand paper and the metal sheet is very large as compared to that between the ordinary paper and the metal sheet. The sand paper is able to remove the outer dull layer from the metal sheet more effectively. Therefore, the metal sheet rubbed with sand paper shines more. The metal sheet rubbed with ordinary paper does not shine much.
24. While travelling on a rickshaw, you might have experienced that if the seat cover is very smooth, you tend to slip when brakes are applied suddenly. Explain.
Ans: Friction is a contact force and is due to roughness of the surfaces. If the seat cover of a rickshaw is very smooth, then the friction between our body and the seat would be very small. We would tend to slip when the brakes of the rickshaw are applied suddenly.
25. Two friends are trying to push a heavy load as shown in Fig.12.5. Suggest a way which will make this task easier for them.
Ans: It would be easier for the friends to roll the load than to slide it. They can put rollers below the heavy load. Rolling friction is smaller than sliding friction. Putting rollers below the heavy load will make the task easier for them.
