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. 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. 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.