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6 questions · timed · auto-graded

Question 12 Marks
Brake handies of motorcycles are generally covered with a towelled cloth.
Answer
Rough towelled cloth on the handles of motrbike provides good grip increasing the friction and we have better control in holding the handles.
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Question 22 Marks
Boats and ships have streamlined shapes.
Answer
Streamlined shapes experience minimum drag (fluid friction) while travelling through air and water. Hence, boats and ships are given streamlined shape.
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Question 32 Marks
Vehicles skid on muddy and wet roads. Suggest what type of tyres can prevent skidding of vehicles.
Answer
Vehicles slip/skid on muddy and wet roads as the roads become smooth and offer less friction to the tyres. Tyres are therefore grooved or treaded to make their surface rough so that the friction between the tyres and the road increases and vehicles may stop easily when desired.
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Question 42 Marks
Define rolling friction and give an example where rolling friction comes into play.
Answer
When we roll an object on a surface, the friction produced between the object and the surface is called rolling friction. Example : when we pull our large suitcases on wheels, rolling friction comes into play. The wheels reduce friction and cut down a lot of effort required to move the suitcase (Rolling friction is less than sliding friction).
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Question 52 Marks
When you push something heavy, the resistance you feel decreases as soon as the object starts moving. Explain the reason.
Answer
It is because when the object is at rest, static friction occurs. The static friction is maximum when the applied force is just short of the force required to start motion between the two bodies in contact. Once the object starts moving, friction (resistance) we feel decreases.
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Question 62 Marks
Write the characteristics of the force of friction.
Answer
Characteristics of force of friction are :

  • Friction opposes the direction of motion.
  • It depends on the nature of the surface that are in contact. Rough surfaces offer greater degree of friction as compared to smooth surfaces. More the roughness of a surface, greater is the friction.
  • Friction depends upon the weight of the object – greater is the weight of the object, greater is frictional force it faces.
  • Friction is independent of area of surface in contact, when the weight remains unchanged.
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