Q. A 5 kg block is placed on a surface with a coefficient of static friction of 0.6. What is the maximum static friction force before the block starts to move?
A.
30 N
B.
20 N
C.
15 N
D.
25 N
Solution
Maximum static friction force = μs * N = 0.6 * (5 kg * 9.8 m/s²) = 29.4 N, approximately 30 N.
Q. A block is at rest on a horizontal surface. If the applied force is gradually increased and reaches the maximum static frictional force, what will happen next?
A.
The block will remain at rest
B.
The block will start moving
C.
The block will accelerate
D.
The block will slide back
Solution
Once the applied force exceeds the maximum static frictional force, the block will start moving.
Q. A block is sliding down a frictionless incline of angle 30 degrees. If the incline has a coefficient of static friction of 0.5, what is the maximum angle at which the block can remain at rest?
A.
30 degrees
B.
45 degrees
C.
60 degrees
D.
90 degrees
Solution
The maximum angle for static friction is given by tan(θ) = μs. Here, θ = tan⁻¹(0.5) which is approximately 26.57 degrees, so the block can remain at rest at angles less than this.
Q. A block is sliding down a frictionless incline of angle θ. If the incline has a coefficient of static friction μs, what is the maximum angle θ for which the block will not slide?
A.
tan⁻¹(μs)
B.
sin⁻¹(μs)
C.
cos⁻¹(μs)
D.
μs
Solution
The block will not slide if the component of gravitational force down the incline is less than or equal to the maximum static friction force, leading to θ = tan⁻¹(μs).
Q. A block is sliding down a frictionless incline. If the incline is now covered with a material that has a coefficient of kinetic friction of 0.3, how does this affect the acceleration of the block?
A.
Increases acceleration
B.
Decreases acceleration
C.
No effect on acceleration
D.
Acceleration becomes zero
Solution
The presence of kinetic friction opposes the motion, thus decreasing the acceleration of the block compared to a frictionless incline.
Q. A block of mass 10 kg is resting on a horizontal surface. If the coefficient of static friction is 0.5, what is the maximum static frictional force acting on the block?
A.
25 N
B.
50 N
C.
75 N
D.
100 N
Solution
Maximum static frictional force (Fs) = μs * N = μs * mg = 0.5 * 10 kg * 9.8 m/s² = 49 N, approximately 50 N.
Q. A block of mass 10 kg is resting on a horizontal surface. If the coefficient of kinetic friction is 0.3, what is the frictional force acting on the block when it is sliding?
A.
30 N
B.
20 N
C.
10 N
D.
15 N
Solution
Frictional force (f_k) = μ_k * N = μ_k * mg = 0.3 * 10 kg * 9.8 m/s² = 29.4 N, approximately 30 N.
Q. A block of mass 5 kg is resting on a horizontal surface. If the coefficient of kinetic friction between the block and the surface is 0.3, what is the frictional force acting on the block when it is sliding?
A.
5 N
B.
10 N
C.
15 N
D.
20 N
Solution
Frictional force (Ff) = μk * N = μk * mg = 0.3 * (5 kg * 10 m/s²) = 15 N.
Q. A block of mass 5 kg is resting on a horizontal surface. If the coefficient of static friction is 0.4, what is the maximum static frictional force acting on the block?
A.
10 N
B.
20 N
C.
15 N
D.
25 N
Solution
Maximum static frictional force (Fs) = μs * N = μs * mg = 0.4 * (5 kg * 10 m/s²) = 20 N.
Q. A block slides down a frictionless incline of angle 30 degrees. If the incline has a coefficient of kinetic friction of 0.2, what is the acceleration of the block?
A.
4.9 m/s²
B.
3.9 m/s²
C.
2.9 m/s²
D.
1.9 m/s²
Solution
Net force = mg sin(30) - μmg cos(30). Acceleration a = (mg sin(30) - μmg cos(30))/m = g(sin(30) - μ cos(30)). Substituting g = 10 m/s² gives a = 10(0.5 - 0.2 * √3/2) = 4.9 m/s².
Q. A box is pushed across a floor with a force of 50 N. If the coefficient of kinetic friction is 0.4, what is the net force acting on the box if the normal force is 100 N?
A.
10 N
B.
20 N
C.
30 N
D.
40 N
Solution
Frictional force = μk * N = 0.4 * 100 N = 40 N. Net force = applied force - frictional force = 50 N - 40 N = 10 N.
Q. A box is pushed with a force of 50 N on a surface with a coefficient of kinetic friction of 0.4. What is the acceleration of the box if its mass is 10 kg?
A.
1 m/s²
B.
2 m/s²
C.
3 m/s²
D.
4 m/s²
Solution
Net force = applied force - frictional force. Frictional force = μ_k * N = 0.4 * 10 kg * 9.8 m/s² = 39.2 N. Net force = 50 N - 39.2 N = 10.8 N. Acceleration = F/m = 10.8 N / 10 kg = 1.08 m/s², approximately 1 m/s².
Q. A box is pushed with a force of 50 N on a surface with a coefficient of kinetic friction of 0.3. If the normal force is 100 N, what is the net force acting on the box?
A.
20 N
B.
30 N
C.
50 N
D.
70 N
Solution
Frictional force = μk * N = 0.3 * 100 N = 30 N. Net force = applied force - frictional force = 50 N - 30 N = 20 N.
Q. A car is moving on a circular track of radius 100 m. If the maximum speed at which it can move without skidding is 20 m/s, what is the coefficient of friction between the tires and the road?
A.
0.1
B.
0.2
C.
0.3
D.
0.4
Solution
The centripetal force required is provided by friction: F = mv^2/r. The frictional force is μmg. Setting them equal gives μ = v^2/(rg). Here, μ = (20^2)/(100*9.8) ≈ 0.4.
Q. A person pushes a box with a force of 30 N, but the box does not move. If the coefficient of static friction is 0.6, what is the maximum static friction force?
A.
18 N
B.
30 N
C.
36 N
D.
60 N
Solution
The maximum static friction force is equal to the applied force when the box does not move, which is 30 N.
Q. If the angle of inclination of a plane increases, what happens to the static frictional force acting on an object resting on the plane?
A.
Increases
B.
Decreases
C.
Remains constant
D.
Becomes zero
Solution
As the angle increases, the component of gravitational force parallel to the plane increases, which can lead to a decrease in static friction until it reaches its maximum value.
Q. If the angle of inclination of a plane increases, what happens to the static friction force acting on an object resting on the plane?
A.
Increases
B.
Decreases
C.
Remains constant
D.
Becomes zero
Solution
As the angle increases, the component of gravitational force parallel to the plane increases, which can lead to a decrease in static friction until it reaches its maximum value.
Q. What is the work done by friction when a 5 kg block slides 2 m on a surface with a coefficient of kinetic friction of 0.4?
A.
-4 N·m
B.
-8 N·m
C.
-10 N·m
D.
-20 N·m
Solution
Frictional force F_friction = μk * N = 0.4 * 5 kg * 9.8 m/s² = 19.6 N. Work done by friction = -F_friction * distance = -19.6 N * 2 m = -39.2 N·m, approximately -40 N·m.
Q. Which of the following factors does NOT affect the coefficient of kinetic friction?
A.
Surface roughness
B.
Normal force
C.
Material of surfaces
D.
Speed of sliding
Solution
The coefficient of kinetic friction is generally independent of the speed of sliding, while it depends on surface roughness, normal force, and material.
Understanding friction is crucial for students preparing for school exams and competitive tests. This fundamental concept not only appears frequently in physics but also forms the basis for many practical applications. By practicing MCQs and objective questions on friction, students can enhance their exam preparation and boost their confidence in tackling important questions effectively.
What You Will Practise Here
Definition and types of friction: static, kinetic, and rolling friction.
Key formulas related to friction, including the coefficient of friction.
Factors affecting friction and their implications in real-world scenarios.
Free body diagrams illustrating forces acting on objects in motion.
Applications of friction in various fields, such as engineering and everyday life.
Numerical problems involving friction to strengthen calculation skills.
Conceptual questions that challenge your understanding of friction principles.
Exam Relevance
The topic of friction is a staple in various examinations, including CBSE, State Boards, NEET, and JEE. Students can expect questions that test their understanding of the principles of friction, often presented in the form of numerical problems or conceptual MCQs. Common question patterns include calculating frictional forces, analyzing scenarios involving different types of friction, and applying theoretical concepts to practical situations.
Common Mistakes Students Make
Confusing static friction with kinetic friction and their respective coefficients.
Neglecting to account for the angle of inclination in friction problems.
Misapplying formulas due to a lack of understanding of the underlying concepts.
Overlooking the role of surface texture and material in friction calculations.
Failing to draw free body diagrams, which can lead to errors in problem-solving.
FAQs
Question: What is the difference between static and kinetic friction? Answer: Static friction acts on objects at rest, preventing them from moving, while kinetic friction acts on moving objects, opposing their motion.
Question: How can I calculate the frictional force? Answer: The frictional force can be calculated using the formula: F_friction = μ * N, where μ is the coefficient of friction and N is the normal force.
Ready to master the concept of friction? Dive into our practice MCQs and test your understanding. Consistent practice with these important friction questions will not only prepare you for exams but also enhance your overall grasp of physics. Start solving now!
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