Limiting Friction

Q.

A block of mass 1 kg lies on a horizontal surface in a truck. The coefficient of static friction between the block and the surface is 0.6. If the acceleration of the truck is 5 ms^-2, the frictional force acting on the block is

1. 7 N

2. 4 N

3. 6 N

4. 5 N

Q.

Two objects A and B each of mass m are connected by a light inextensible string. They are restricted to move on a frictionless ring of radius R in a vertical plane (as shown in figure). The objects are released from rest at the position shown. Then, the tension in the cord just after release is

1. 

2. 

3. zero

4. mg

Q. Minimum horizontal force $F$ required to keep the smaller block stationary with respect to the bigger block as shown in the figure is :

1. $\frac{(M-m)g}{\mu }$
2. $\frac{(M+m)g}{\mu }$
3. $\frac{Mg}{\mu }$
4. $\frac{mg}{\mu }$

Q. Assertion: On a rainy day it is difficult to drive a car or bus at high speed.
Reason: The value of coefficient of friction is lowered due to wetting of the surface.

1. Both Assertion and Reason are correct and Reasion is the correct explanation for Assertion
2. Both Assertion and Reason are correct but Reasion is not the correct explanation for Assertion
3. Assertion is correct but Reason is incorrect
4. Both Assertion and Reason are incorrect

Q.

A light string is warped around a cylindrical log of wood which is placed on a horizontal surface with its axis vertical and it is pulled with a constant force $F$ as shown in the figure. (Friction is absent everywhere).

1. Tension $T$ in string will increase with increase in $\theta$.

2. Tension $T$ in string will decrease with increase in $\theta$.

3. Tension $T>F$ if $\theta >\frac{\pi }{3}$

4. Tension $T>F$ if $\theta >\frac{\pi }{4}$

Q.

A box is lying on an inclined plane what is the coefficient of static friction if the box starts sliding when an angle of inclination is $60°$?

1. $1.173$

2. $1.732$

3. $2.732$

4. $1.677$

Q. Two blocks of equal masses $M$ are connected by a string and are kept on a rough horizontal surface as shown in the figure. $\mu$ is the coefficient of friction between the blocks and the surface. If $0<F_1-F_2<2\mu Mg$ , then choose the correct statement.

1. The direction of friction on block $A$ is towards right.
2. The direction of friction on block $B$ is either towards left or right
3. Tension in the string is zero
4. Friction force on block $B$ is zero

Q. Mark the incorrect statements about the frictionbetween two bodies.(1) Limiting friction is never less than staticfriction(2) Limiting friction is greater than. the kineticfriction(3) Static friction is always greater than thekinetic friction(4) Coefficient of static friction is greater than thecoefficient of kinetic friction

Q.

A block of mass m is kept over another block of mass $M$ and the system rests on a horizontal surface. A constant horizontal force $F$ acting on the lower block produces acceleration $\frac{F}{2(m+M)}$ in the system, the two blocks always move together. Find the work done by the force of friction on the smaller block by the bigger block during a displacement d of the system.

1. 

2. 

3. 

4. 

Q. 72.A block of mass 0.5kg rests against a wall exerting a horizontal force of 15N on the wall. If the coefficient of friction between the wall and the block is 0.5 then the frictional force acting on the block will be

Q. Three blocks of masses $2\text{kg}$, $4\text{kg}$ and $6\text{kg}$ arranged as shown in figure connected by string on a frictionless incline of ${37}^{\circ }$. A force of $120\text{N}$ is applied upward along the incline to the uppermost block. The cords are light. The tensions $T_1$ and $T_2$ in the strings are $(g=10{\text{m/s}}^2,\sin {37}^{\circ }=\frac{3}{5})$

1. $T_2=60\text{N}$
2. $T_2=36\text{N}$
3. $T_1=8\text{N}$
4. $T_1=20\text{N}$

Q. Why is it easier to pull than to push a lawn roller?

Q.

what is coefficient of static friction?

Q. The retarding acceleration of $7.35m/s^2$ due to frictioanl forcer stops the car of mass $400kg$ travelling on road. The coefficient of friction between the tyre of the car and the road is

1. $0.55$
2. $0.75$
3. $0.70$
4. $0.65$

Q. A 1 kg block situated on a rough incline is connected to a spring of spring constant 100Nm−1100Nm−1 as shown. The block is released from rest with the spring in the unstretched position. The block moves $10cm$ down the incline before coming to rest. Find the coefficient of friction between the block and the incline. Assume that the spring has a negligible mass and the pulley is frictionless.

Q. A block is in contact with the inner wall of a hollow cylindrical drum as shown in figure. The minimum angular velocity (in $\text{rad/s}$) needed for the cylinder to keep the block stationary relative to itself, when the cylinder is vertical and rotating about its axis will be

Q. 21. An insect crawls inside a hemisphere of radius 10 cm. If the coefficient of friction between the insect and the surface is 1/1.414. Then find out the maximum angle upto which the insect can remain static?

Q. A block of mass $10kg$ is kept on an inclined plane having an angle of inclination ${37}^{\circ }$ attached with a spring of force constant $20N/m$ as shown in the figure. If the coefficient of friction between block and incline is $0.8$, then the maximum value of elongation for which the block is in contact with the inclined plane and has no slipping is

1. $0.3\text{m}$
2. $0.156\text{m}$
3. $2\text{m}$
4. $6.66\text{m}$

Q. an unbanked curved has a radius of 60m The maximium speed at which a car makes a trun if the cofficient of static friction is 0.75 is

Q. A horizontal force of $10\text{N}$ is necessary to just hold a block stationary against a wall as shown in the figure. The weight of the block is $2\text{N}$. The coefficient of friction $\mu$, between the block and the wall is

1. $0.30$
2. $0.20$
3. $0.25$
4. $0.35$

Q. In the figure shown, find the acceleration in $m/s^2$ of the body kept on the rough horizontal surface. Take $g=10m/s^2$.

Q. A turn of radius $20m$ is banked for the vehicles going at a speed of $36km/h$. If the coefficient of static friction between the road and the tyre is $0.4$. What are the possible speed of a vehicle so that is neither slips down nor skids up then?

1. 14.74
2. 66
3. 88
4. 99

Q. Two blocks of equal masses $M$ are connected by a string and are kept on a rough horizontal surface as shown in the figure. $\mu$ is the coefficient of friction between the blocks and the surface. If $0<F_1-F_2<2\mu Mg$ , then choose the correct statement.

1. The direction of friction on block $A$ is towards right.
2. The direction of friction on block $B$ is either towards left or right
3. Tension in the string is zero
4. Friction force on block $B$ is zero

Q. A It is difficult to start the motion of a body on a rough surface, rather than tomaintain the motion of the body. R: Static friction is always greater than thekinetic friction.

Q. In the shown figure, a man on a horizontal platform $A$, kept on a smooth horizontal surface, holds a rope attached to a box $B$. Man pulls the rope with a constant force of $50\text{N}$. The co-efficient of friction between the man and the platform is $0.5$. Then (Mass of man is $80kg$, mass of platform is $120kg$ and mass of box is $100kg$)

1. velocity of box relative to platform after $4s$ is $3m/s$.
2. velocity of man relative to platform after $4s$ is $2m/s$.
3. friction force between man and platform is $40N$.
4. friction force between man and platform is $30N$.

Q. If we say static friction while comparing with kinetic friction that means we arent including limiting friction under static friction?

Q. Assertion: On a rainy day it is difficult to drive a car or bus at high speed.
Reason: The value of coefficient of friction is lowered due to wetting of the surface.

1. Both Assertion and Reason are correct and Reasion is the correct explanation for Assertion
2. Both Assertion and Reason are correct but Reasion is not the correct explanation for Assertion
3. Assertion is correct but Reason is incorrect
4. Both Assertion and Reason are incorrect

Q. An automobile is turning around a circular road of radius, $r$. The coefficient of friction between the tyres and the road is $\mu$. The velocity of the vehicle should not be more than

1. $\sqrt{\frac{\mu g}{r}}$
2. $\sqrt{\mu rg}$
3. $\mu rg$
4. $\mu g/r$

Q. Find the minimum value of coefficient of friction between the $4kg$ block and the surface for the system to be at rest for the figure shown.

1. $0.4$
2. $0.5$
3. $0.6$
4. $0.75$

Q. A marble block of mass $2kg$ lying on ice when given a velocity of $6m/s$ is stopped by friction in $10s$. Then the coefficient of friction is

1. $0.01$
2. $0.02$
3. $0.03$
4. $0.06$