Get important questions and answers of Friction for Board exams. View 11th Physics important questions for exam point of view developed by the top IITian faculties from Kota. These important questions and answers will play significant role in clearing concepts of Friction for Class 11and also in revision for Class 12 students. This question bank is designed by keeping NCERT in mind.
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Q. Automobile tires are generally provided with irregular projection over their surface why?
Sol. To increase friction.
Q. What does happen to coefficient of friction when weight of body doubled?
Sol. It remains same.
Q. Why synthetic rubber is preferred in tyres making?
Sol. Coefficient of friction between road and synthetic rubber is large.
Q. Is it reasonable to expect the coefficient of friction to exceed unity?
Sol. In case of normal plane surface the coefficient of friction is less than unity, but when the surfaces are so irregular that sharp minute projection and cavities exist on the surface. The coefficient friction may exceed
Q. What is the angle of friction between two surface in contact having coefficient of friction .
Sol. $\theta=\tan ^{-1}(\mu)=\tan ^{-1}(1 / \sqrt{3})=30^{\circ}$ where $\theta=$ friction angle $\mu=$ coefficient of friction.
Q. Sand is thrown on track covered with snow in hilly area, why?
Sol. Sand is thrown on snow to increase the force of friction, so that tyres of the vehicles may not slip over the snow.
Q. When a wheel is rolling on a road, what is the direction of the frictional force between the wheel and the road?
Sol. As the wheel rolls forward the part of the wheel in contact of the road slides backward hence the force of friction acts in the forward direction along the tangent to the surface of the road and the part of the wheel in contact.
Q. How does lubricant help in minimizing friction?
Sol. The lubricant forms a thin layer between the two surface in contact. Thus sliding friction is replaced by liquid friction which is much smaller.
Q. Why are ball bearings are used to reduce friction
Sol. Because ball bearing convert sliding friction into rolling friction.
Q. There is a limit beyond which further polishing of surface increase rather than decrease frictional resistance why?
Sol. Normally friction decreases when smoothness of surface increases however, when surface in contact are made too smooth then binding force of adhesion increase which increases friction. This phenomena is called cold welding.
Q. How do we save petrol by keeping the rubber tyres of our vehicle fully inflated.
Sol. The weight of the vehicle and its occupants cause some flattening of the part of the wheel in contact with the ground and make some hollow space in the ground hence work is done in lifting the wheel Less work would be done if the rubber wheels are hard that is fully inflated. When they will be flattened less, less work would require less consumption of fuel per unit distance covered.
Q. Friction is a necessary evil, comment.
Sol. Friction is called a necessary evil. It is necessary because we cannot do without it. At the same time it is an evil because it involves unnecessary wastage of energy. The following facts make the point clear Friction is a necessity
Q. What is the law of friction.
Sol. There are five laws of friction.
(1)The direction of the force of limiting friction is always opposite to the direction in which the motion takes place or tend to take place.
(2) The force of friction acts tangentially along the surface of contact of two bodies.
(3) The magnitude of the limiting force of friction (F) is directly proportional to the normal reaction (R) between the two surface. i.e. F µ R.
(4) Force of limiting friction is independent of the area of the surface of contact of two bodies as long as normal reaction is constant.
(5) The force of limiting friction depends on the nature of the surfaces in contact.
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