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Two blocks masses 1 kg and 2 kg rest on a smooth horizontal table. When the 2 kg block is pulled by a certain force F, the tension T in the string is 1.5 N. The value of F is


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Important Questions on Friction

MEDIUM
A block A of mass m1 rests on a horizontal table. A light string connected to it passes over a frictionless pulley at the edge of table and from its other end another block B of mass m2 is suspended. The coefficient of kinetic friction between the block and the table is μk. When the block B is sliding on the table, the tension in string is:
MEDIUM
A car is negotiating a curved road of radius R . The road is banked at an angle θ. The coefficient of friction between the tyres of the car and the road is μs. The maximum safe velocity on this road is:
MEDIUM
A plank with a box on it at one end is gradually raised about the other end. As the angle of inclination with the horizontal reaches 30°, the box starts to slip and slides 4.0 m down the plank in 4.0 s. The coefficients of static and kinetic friction between the box and the plank will be, respectively:
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MEDIUM

Consider the system shown below.

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A horizontal force F is applied to a block X of mass 8 kg such that the block Y of mass 2 kg adjacent to it does not slip downwards under gravity. There is no friction between the horizontal plane and the base of the block X. The coefficient of friction between the surfaces of the blocks X and Y is 0.5. Take acceleration due to gravity to be 10 m s-2. The minimum value of F is

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Two blocks (m=0.5 kg and M=4.5 kg) are arranged on a horizontal frictionless table as shown in the figure. The coefficient of static friction between the two blocks is 37. Then the maximum horizontal force that can be applied on the larger block so that the blocks move together is N. (Round off to the Nearest Integer) [Take g as 9.8 m s-2]

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HARD
A small box resting on one edge of the table is struck in such a way that it slides off the other edge, 1 m away, after 2 seconds. The coefficient of kinetic friction between the box and the table
EASY
A block kept on a rough inclined plane, as shown in the figure, remains at rest upto a maximum force 2 N down the inclined plane. The maximum external force up the inclined plane that does not move the block is 10 N. The coefficient of static friction between the block and the plane is: [Take g=10 m s-2 ]
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HARD

A block of mass 5 kg is (i) pushed in case A and (ii) pulled in case B, by a force F=20 N, making an angle of 30o with the horizontal, as shown in the figures. The coefficient of friction between the block and floor is μ=0.2. The difference between the accelerations of the block, in case B and case A will be:
g=10m s-2
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HARD
A box of mass 10 kg is placed near the rear end of a long flat trolley such that it is 2 m from its rear end. The coefficient of friction between the box and the trolley surface is 0.2. Starting from rest, the trolley is given a uniform acceleration of 3 m s-2. How much distance will the trolley cover by the time the box fell off from the trolley? g=10 m s-2
MEDIUM

A system of two blocks of masses m=2 kg and M=8 kg is placed on a smooth table as shown in figure. The coefficient of static friction between two blocks is 0.5. The maximum horizontal force F that can be applied to the block of mass M so that the blocks move together will be g=9.8 m s-2

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EASY
A block A of mass 4 kg is placed on another block B of mass 5 kg, and the block B rests on a smooth horizontal table. If the minimum force that can be applied on A so that both the blocks move together is 12 N, the maximum force that can be applied on B for the blocks to move together will be :
MEDIUM

A block of mass 5 kg resting on a horizontal surface is connected by a cord, passing over a light frictionless pulley to a hanging block of mass 5 kg. The coefficient of kinetic friction between the block and the surface is 0.5. Tension in the cord is g=9.8 m s-2

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MEDIUM
A block of mass m is placed on a surface with a vertical cross section given by y=x36. If the coefficient of friction is 0.5, the maximum height above the ground at which the block can be placed without slipping is 
HARD
A box when dropped from a certain height reaches the ground with a speed v . When it slides from rest from the same height down a rough inclined plane inclined at an angle 45o to the horizontal, it reaches the ground with a speed v3 . The coefficient of sliding friction between the box and the plane is (acceleration due to gravity is 10 m s-2 )
MEDIUM
A heavy box is to be dragged along a rough horizontal floor. To do so, the person A pushes it at an angle 30° from the horizontal and requires a minimum force FA, while the person B pulls the box at an angle 60° from the horizontal and needs minimum force FB. If the coefficient of friction between the box and the floor is 35, the ratio FAFB is
MEDIUM

A block of mass 5 kg is kept against an accelerating wedge with a wedge angle of 45° to the horizontal. The co-efficient of friction between the block and the wedge is μ=0.4. What is the minimum absolute value of the acceleration of the wedge to keep the block steady. Assume g=10 m s-2

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HARD
Put a uniform meter scale horizontally on your extended index fingers with the left one at 0.00 cm and the right one at 90.00 cm. When you attempt to move both the fingers slowly towards the center, initially only the left finger slips with respect to the scale and the right finger does not. After some distance, the left finger stops and the right one starts slipping. Then the right finger stops at a distance xR from the center (50.00 cm) of the scale and the left one starts slipping again. This happens because of the difference in the frictional forces on the two fingers. If the coefficients of static and dynamic friction between the fingers and the scale are 0.40 and 0.32, respectively, the value of xR (in cm) is___________.
EASY
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Given in the figure are two blocks A and B of weight 20 N and 100 N, respectively. These are being pressed against a wall by a force F and kept in equilibrium as shown. If the coefficient of friction between the blocks is 0.1 and between block B and the wall is 0.15, the frictional force applied by the wall on block B is:
HARD
A block of mass m2 is placed on a horizontal table and another block of mass m1 is placed on top of it. An increasing horizontal force F=αt is exerted on the upper block but the lower block never moves as a result. If the coefficient of friction between the blocks is μ1 and that between the lower block and the table is μ2, then what is the maximum possible value of μ1/μ2?
HARD
A system consists of three masses m1, m2 and m3 connected by a string passing over a pulley P. The mass m3 hangs freely and m2 and m1 are on a rough horizontal table (the coefficient of friction =μ). The pulley is frictionless and of negligible mass. The downward acceleration of mass m3 is: (Assume m1=m2=m3=m)
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