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Which of the following statements regarding laws governing the friction between dry surfaces are correct? 1. The friction force is dependent on the velocity of sliding.  2. The friction force is directly proportional to the normal force. 3. The friction force is dependent on the materials of the contact surfaces. 4. The Friction force is independent of the area of contact surfaces.
Which of the following is NOT true about Frictional force? A. Friction is the force which opposes the relative motion of two surfaces in contact. B. The force of friction that acts when a body is moving (sliding) on a surface is called sliding friction. C. Friction in machines wastes energy and also causes wear and tear. D. Rolling friction is much more than sliding friction, the use of ball bearings in a machine considerably reduces friction.
Which one of them is a correct combination? 1) Boundary Lubrication i) Dimensionless film thickness < 1 2) Hydrodynamic Lubrication ii) Dimensionless film thickness lies between 1 and 3 3) Mixed Lubrication iii) Dimensionless film thickness lies between 3 and 5 4) Elastohydrodynamic Lubrication iv) Dimensionless film thickness is greater than 5
While discussing about friction, a teacher gave a number of examples to explain the concept. Some of the examples where friction is useful in our day-to-day life as quoted by the teacher are given below : A. We are able to write because of friction between the tip of the pen and the paper. B. We are able to walk because of friction between our feet and the ground. C. A ball thrown vertically upwards comes back to us due to friction. D. We are able to stop a moving vehicle by applying brakes because of friction. The correct examples were
Consider the following statements: 1. The kinetic friction is always less than the rolling friction. 2. The kinetic friction is always equal to the rolling friction. 3. The kinetic friction is always greater than the rolling friction. Which of the following statement is correct?
Which of the following statements is/are correct concerning Friction? 1. Static friction supports the impending motion.  2. Friction is the component of the contact force parallel to the surfaces in contact, which opposes impending or actual relative motion between the two surfaces. Select the correct answer using the code given below.
A multiple disc clutch has five plates having four pairs of active friction surfaces. If the intensity of pressure is not to exceed 0.127 N/mm2, find the power transmitted at 500 r.p.m. The outer and inner radii of friction surfaces are 125 mm and 75 mm respectively. Assume uniform wear and take coefficient of friction = 0.3.
Which of the following is correct about friction? I. Rolling friction is smaller than the sliding friction II. Sliding friction is smaller than static friction 
A cube of side 4 cm is painted black on the pair of one opposite surfaces, blue on the pair of another opposite surfaces and red on remaining pair of opposite surfaces. The cube is now divided into smaller cubes of equal side of 1 cm each. How many smaller cubes have two surfaces painted?
An air conditioner can cool the hall in 40 miutes while another takes 45 minutes to cool under similar conditions. If both air conditioners are switched on at same instance then how long will it take to cool the room approximately ?