## Class 11 Physics Friction Multiple Choice Questions And Answers

**Question 1. During the acceleration of a bicycle, the direction of the force of static friction, exerted by the ground on the wheels is**

- Against the direction of motion of the front wheel, and along the direction of motion of the rear wheel
- Along the motion of the front wheel, and against the motion of the rear wheel
- Against the motion of both the wheels
- Along the motion of both the wheels

**Answer:** 1. Against the direction of motion of the front wheel, and along the direction of motion of the rear wheel

**Question 2. A block of mass 0.1 kg is kept pressed against a wall, by applying a force of 5 N horizontally on the block. The coefficient of friction between the block and the wall is 0.5. Friction acting on the block is**

- 2.5 N
- 0.98 N
- 4.9 N
- 0.49 N

**Answer:** 2. 0.98 N

**Question 3. A piece of stone of mass 1 kg slides over ice at 2 m · s ^{-1} and comes to rest in 10 s. In this case, the frictional force is**

- 0.2N
- 20N
- 10N
- 1N

**Answer:** 1. 0.2N

**Question 4. A uniform chain of length l is lying on a rough table and 1/nth of its length is hanging from the table’s edge. If the chain is about to slide off the table, the coefficient of friction between the chain and the table is**

- \(\frac{1}{n}\)
- \(\frac{1}{n-1}\)
- \(\frac{1}{n+1}\)
- \(\frac{n-1}{n+1}\)

**Answer:** 2. \(\frac{1}{n-1}\)

**Question 5. If the coefficient of friction is 1/√3, the height up to which a particle can rise and stay inside a hollow sphere of radius r, is (the inner surface of the sphere is rough)**

- 0.5 r
- 0.75 r
- 0.95 r
- 0.134 r

**Answer:** 4. 0.134 r

**Question 6. A block of mass 5 kg is placed on a rough horizontal surface. The coefficients of static and sliding friction between the body and the surface are 0.7 and 0.5 respectively. A horizontal force is applied on the block so that the block just starts moving. If the applied force continues to act even after the block is set in motion, the acceleration of the block will be [g = 10 m · s ^{-2}]**

- 1 m s
^{-2} - 2 m s
^{-2} - 3 m s
^{-2} - 4 m s
^{-2}

**Answer:** 2. 2 m s^{-2}

**Question 7. Graphs below show the variation of the frictional force, against the force on a block, applied parallel to the surface of contact of the block with a rough horizontal plane. Out of 1, 2, 3, 4 which one is the correct graph?**

**Answer:** 2

**Question 8. A tram is moving with an acceleration of 49 cm · s ^{-2}. If 50% of the engine power is used up to overcome friction, and the remaining 50% is spent for increasing velocity, the coefficient of friction between the wheel and the track should be**

- 0.03
- 0.02
- 0.05
- 0.10

**Answer:** 3. 0.05

**Question 9. There is no slipping between the two blocks shown. What is the force of friction between the blocks?**

- Zero
- 9N
- 12 N
- 6N

**Answer:** 4. 6N

**Question 10. A block of weight 5 N is pushed against a vertical wall by a force of 12 N. The coefficient of friction between the wall and the block is 0.6. The magnitude of the force exerted by the wall on the block is**

- 12 N
- 5N
- 7.2 N
- 13 N

**Answer:** 3. 7.2 N

**Question 11. In order to stop a car in the shortest distance on a horizontal road, one should**

- Apply the brakes very hard so that the wheels stop rotating
- Apply the brakes hard enough to just prevent slipping
- Pump the brakes (press and release)
- Shut the engine off and do not apply brakes

**Answer:** 2. Apply the brakes hard enough to just prevent slipping

**Question 12. A boy of mass M is applying a horizontal force to slide a box of mass M’ on a rough horizontal surface. The coefficient of friction between the shoes of the boy and the floor is μ and that between the box and the floor is μ’. In which of the following cases it is certainly not possible to slide the box?**

- μ<μ’, M< M’
- μ> μ’, M<M’
- μ < μ’, M>M’
- μ>μ’, M>M’

**Answer:** 1. μ < μ’, M< M

**Question 13. Angle of an inclined plane with the horizontal is θ. The first half of the plane is smooth and the other half is rough. When a body is released from the top of the plane, it slides down and comes to rest at the bottom. The coefficient of friction between the body and the inclined plane is**

- μ = 2 tanθ
- μ = tanθ
- \(\mu=\frac{2}{\tan \theta}\)
- \(\mu=\frac{1}{\tan \theta}\)

**Answer:** 1. μ = 2 tanθ

**Question 14. Two blocks of masses m _{1} = 5 kg and m_{2} = 6 kg, are connected by a weightless frictionless string passing over a pulley and are kept as shown. While m2 is hanging vertically, is resting on an incline.**

**The angle of inclination θ = 30°. In this case, the magnitude and direction of the frictional force on mass m _{1}, are [g = 10 m ·s^{-2}]**

- 35 N, upward along the inclined plane
- 35 N, downward along the inclined plane
- 85 N, upward along the inclined plane
- 85 N, downward along the inclined plane

**Answer:** 2. 35 N, downward along the inclined plane

**Question 15. A body slides down an inclined plane of inclination θ. While sliding downwards, the coefficient of friction is directly proportional to the displacement. The body slides down the plane with a**

- Constant acceleration g sinθ
- Constant acceleration (g sinθ – μg cosθ)
- Constant retardation (μg cosθ – g sinθ)
- Variable acceleration

**Answer:** 4. Variable acceleration

**Question 16. For an object sliding on a plane, the force of friction is less if the plane is inclined, instead of being horizontal, because,**

- The coefficient of friction decreases
- Normal force decreases
- Effective mass decreases
- For an angle of inclination θ, friction is inversely proportional to tan θ

**Answer:** 2. Normal force decreases

**Question 17. A body of mass m is pushed up with a velocity u along a plane of inclination θ. If the coefficient of friction between the body and the inclined plane is μ, displacement of the body before coming to rest is then the maximum inclination of the plane with the horizontal is**

- \(\frac{u^2 \mu}{2 g \sin \theta}\)
- \(\frac{u^2 \mu}{2 g \cos \theta}\)
- \(\frac{u^2}{4 g \sin \theta}\)
- \(\frac{u^2}{4 g \cos \theta}\)

**Answer:** 3. \(\frac{u^2}{4 g \sin \theta}\)

**Question 18. A mass placed on an inclined plane is just in equilibrium. If μ is the coefficient of friction of the surface, then the maximum inclination of the plane with the horizontal is**

- tan
^{-1}μ - tan
^{-1}(μ/2) - sin
^{-1}μ - cos
^{-1}μ

**Answer:** 1. tan^{-1}μ

**Question 19. A 13 m ladder is placed against a smooth vertical wall with its lower end 5 m from the wall. What should be the minimum coefficient of friction between the ladder and the floor so that it remains in equilibrium?**

- 0.36
- 0.72
- 0.21
- 0.52

**Answer:** 3. 0.21

**Question 20. A box of mass 8 kg is placed on a rough inclined plane of inclination θ. Its downward motion can be prevented by applying an upward pull F and it can be made to slide upwards by applying a force 2 F. The coefficient of friction between the box and the inclined plane is**

- 1/3 tanθ
- 3tanθ
- 1/2tanθ
- 2tanθ

**Answer:** 1. 1/3 tanθ

**In this type of question, more than one option are correct.**

**Question 21. Three blocks are arranged as shown. The whole system is placed on a smooth horizontal plane. The coefficient of friction between the plane and the 5 kg block is 0.1, between the 5kg block and 3kg block is a smooth horizontal surface of 0.1, and between the 3 kg and 2 kg block is 0.2. The total frictional force on the 3 kg block is**

- Towards right
- Towards left
- Zero
- Non zero

**Answer:**

2. Towards the left

4. Non-zero

**Question 22. If the force of friction is equal to the force applied, then friction may be**

- Static
- Kinetic
- Limiting
- No conclusions can be drawn

**Answer:**

1. Static

3. Limiting

**Question 23. If the object is at rest, then friction may be**

- Static
- Kinetic
- Limiting
- No conclusion can be drawn

**Answer:**

1. Static

3. Limiting

**Question 24. Two particles A and B, each of mass m are kept stationary by applying a horizontal force F = mg on particle B as shown. Then**

- tanβ = 2 tanα
- 2T
_{1}= 5T_{2} - √2T
_{1}= √5T_{2} - None of these

**Answer:**

1. tan/3 = 2 tan

3. √2T_{1} = √5T_{2}

**Question 25. Mark the correct statements about the friction between two bodies.**

- Static friction is always greater than kinetic friction
- The coefficient of static friction is always greater than the coefficient of kinetic friction
- Limiting static friction is always greater than kinetic friction.
- Limiting friction is never less than static friction

**Answer:**

2. The coefficient of static friction is always greater than the coefficient of kinetic friction

3. Limiting static friction is always greater than the kinetic friction.

4. Limiting friction is never less than static friction