A boat or an aeroplane has a pointed or tapering front / head. Why?

To increase the friction of fluid

To reduce the friction of fluid

Limiting friction of a body depends on _____

The periphery of the contact surfaces

The volume of the smaller body on larger surface

The periphery of the contact surfaces

What are the types of kinetic friction?

Rolling friction and adhesive friction

Sliding friction, rolling friction and adhesive friction

Sliding friction and rolling friction

Rolling friction and adhesive friction

Sliding friction and adhesive friction

Identify the wrong statement about a single plate clutch from the following.

Torque is transmitted by friction coupling

It transmits power from the flywheel to transmission shaft

Power is transmitted by a cone on the transmission shaft engaging with a tapered recess in the flywheel

Torque is transmitted by friction coupling

It is placed between the engine and the gearbox in case of automobiles

A trenched conical pivot bearing has semi-cone angle α and the two radii are r1 and r2 respectively with r1 > r2. The coefficient of friction between the sliding surfaces is μ. For an axial thrust load of W kN, the reduction in torque due to friction (assuming uniform rate of wear) is

\(\frac{3}{2}\mu W\left[ {\frac{{{{\left( {{r_1}} \right)}^3} - {{\left( {{r_2}} \right)}^3}}}{3}} \right]cosec\;\alpha \)

\(\frac{1}{2}\mu W\left( {{r_1} + {r_2}} \right)\;cosec\;\alpha \)

\(\frac{3}{2}\mu W\left[ {\frac{{{{\left( {{r_1}} \right)}^3} - {{\left( {{r_2}} \right)}^3}}}{3}} \right]cosec\;\alpha \)

\(\frac{2}{3}\mu W\left[ {\frac{{{{\left( {{r_1}} \right)}^3} - {{\left( {{r_2}} \right)}^3}}}{3}} \right]cosec\;\alpha \)

Considering the safe design, friction clutch should be designed:

either uniform pressure (or) uniform wear

Uniform pressure for high torque and uniform wear for low torque

If the stiffness of a spring of centrifugal clutch is increased, it causes:

increase the friction torque at maximum speed

40 + Mcqs in Friction in Engineering Mechanics Page 1 McqOptions

1.	Sliding friction is _________ than / to rolling friction
A.	smaller
B.	greater
C.	equal
D.	None of the above
Answer» B. greater

Discussion

2.	Four children were asked to arrange forces due to rolling, static and sliding frictions in a increasing order. Their arrangements are given below. Choose the correct arrangement.
A.	Rolling, Static, Sliding
B.	Static, Rolling, Sliding
C.	Rolling, sliding, static
D.	Sliding, Static, Rolling
Answer» D. Sliding, Static, Rolling

Discussion

3.	The frictional force exerted by fluids is also called ______
A.	drug
B.	drag
C.	drop
D.	drown
Answer» C. drop

Discussion

4.	The sole of the shoes becomes plain after wearing it for several months. The reason is
A.	Wearing out due to friction
B.	Wearing out due to no friction
C.	Sole is of bad quality
D.	None of the above
Answer» B. Wearing out due to no friction

Discussion

5.	A boat or an aeroplane has a pointed or tapering front / head. Why?
A.	To increase the friction of fluid
B.	To reduce the friction of fluid
C.	To look good
D.	For no reason
Answer» C. To look good

Discussion

6.	Tyres are treaded to
A.	To look good
B.	Increase friction
C.	To increase its longivity
D.	To increase weight of the tyre
Answer» C. To increase its longivity

Discussion

7.	Spring balance is a device used for measuring the _____________ acting on an object.
A.	mass
B.	pressure
C.	force
D.	None of the above
Answer» D. None of the above

Discussion

8.	Lubricants are substances which
A.	Increases friction
B.	Are used to light fire
C.	Reduces friction
D.	Are used to put off fire
Answer» D. Are used to put off fire

Discussion

9.	It is difficult to walk on any oily floor because
A.	Floor gets spoiled
B.	There is more resistance
C.	Force of friction is high
D.	Force of friction is very less
Answer» E.

Discussion

10.	A matchstick struck on a matchbox catches fire easily because
A.	Friction may cause fire
B.	Of chemical reaction
C.	Force heated the match stick
D.	None of the above
Answer» B. Of chemical reaction

Discussion

11.	The value of the frictional force for a body is always constant when it is static and does not vary with applied force.
A.	True
B.	False
Answer» C.

Discussion

12.	Consider a block of mass 9.81kg on an inclined surface of the coefficient of friction 0.15 and angle of inclination 30 degrees. What will be its acceleration on the inclined plane if acceleration due to gravity is 9.81 m/s2?
A.	3.63 m/s2
B.	4.63 m/s2
C.	9.81 m/s2
D.	10 m/s2
Answer» E.

Discussion

13.	Limiting friction of a body depends on _____
A.	Area of contact of surfaces
B.	The volume of the smaller body on larger surface
C.	Nature of surfaces
D.	The periphery of the contact surfaces
Answer» D. The periphery of the contact surfaces

Discussion

14.	If a box is lying on the floor of a wagon with a coefficient of friction 0.2, what is the maximum acceleration of the wagon for which the box would remain stationary? (Let g = 9.81 m/s2)
A.	1.96 m/s2
B.	2 m/s2
C.	3.92 m/s2
D.	4 m/s2
Answer» B. 2 m/s2

Discussion

15.	_____ is known as the motion that would take place under the applied force if friction were absent.
A.	Impending motion
B.	Constrained motion
C.	Unconstrained motion
D.	Linear motion
Answer» B. Constrained motion

Discussion

16.	For a body of mass “m” on a rough inclined plane with a constant but arbitrary coefficient of friction as shown in the figure, what is the acceleration on the inclined plane if the net downward force is donated as “F”. Let “g” be the acceleration due to gravity and “u” be the coefficient of friction.
A.	g x sin θ
B.	g x cos θ
C.	g (sin θ – u cos θ)
D.	g (cos θ – u sin θ)
Answer» D. g (cos θ – u sin θ)

Discussion

17.	For a body of mass “m” on a rough inclined plane with a constant but arbitrary coefficient of friction as shown in the figure, what is the angle of repose if the net downward force is donated as “F”. Let “g” be the acceleration due to gravity and “u” be the coefficient of friction.
A.	sin θ
B.	cos θ
C.	tan θ
D.	cot θ
Answer» D. cot θ

Discussion

18.	The maximum value of static friction when the body is at the verge of starting motion is known as _____
A.	Static friction
B.	Limiting friction
C.	Impending motion
D.	Angle of repose
Answer» C. Impending motion

Discussion

19.	What are the types of kinetic friction?
A.	Sliding friction, rolling friction and adhesive friction
B.	Sliding friction and rolling friction
C.	Rolling friction and adhesive friction
D.	Sliding friction and adhesive friction
Answer» C. Rolling friction and adhesive friction

Discussion

20.	Static coefficient of friction is greater than the kinetic coefficient of friction.
A.	True
B.	False
Answer» B. False

Discussion

21.	If there are n1 discs on the driving shaft and n2 discs on the driven shaft in a multi-plate clutch, then the number of pairs of contact surface is
A.	n1 + n2
B.	n1 + n2 - 1
C.	n1 + n2 + 1
D.	n1 + n2 + 2
Answer» C. n1 + n2 + 1

Discussion

22.	A disc clutch is required to transmit 5 kW at 2000 rpm. The disc has a friction lining with the coefficient of friction 0.25. The bore radius of the friction lining is 25 mm. Assume uniform contact pressure of 1 MPa. The value of outside radius of the friction lining in mm is:
A.	59.3
B.	39.4
C.	29.6
D.	49.5
Answer» C. 29.6

Discussion

23.	In the multiple disc clutch, if there are 6 discs on the driving shaft and 5 discs on the driven shaft, then the number of pairs of contact surfaces will be equal to
A.	11
B.	12
C.	10
D.	22
Answer» D. 22

Discussion

24.	A multi-disc clutch employs 3 steel and 2 bronze discs having outer diameter of 300 mm and inner diameter of 175 mm. If the coefficient of friction is 0.25 and axial force on each pair of surfaces is 5 kN, then the torque transmitted (assuming uniform wear) is
A.	416.6 N m
B.	887.5 N m
C.	1093.75 N m
D.	593.75 N m
Answer» E.

Discussion

25.	In a multiple–disc clutch, the axial intensity of pressure is not to exceed 0.2 MPa. The inner radius of the discs is 100 mm and is half the outer radius. The axial force per pair of contact surfaces in N is
A.	2000 π
B.	3000 π
C.	4000 π
D.	6000 π
Answer» D. 6000 π

Discussion

26.	In case of the design of friction clutches, the uniform rate of wear theory is used over uniform pressure. The reasons may be the following:1. It gives higher frictional torque.2. It gives lower frictional torque.3. The intensity of pressure is maximum at the inner radius and minimum at the outer radius of the friction or contact surfaces.4. This concept is prevalent for running and old clutches.Which of the above reasons is correct?
A.	1, 3 and 4
B.	1 and 3 only
C.	2 and 3
D.	2 and 4
Answer» B. 1 and 3 only

Discussion

27.	Identify the wrong statement about a single plate clutch from the following.
A.	It transmits power from the flywheel to transmission shaft
B.	Power is transmitted by a cone on the transmission shaft engaging with a tapered recess in the flywheel
C.	Torque is transmitted by friction coupling
D.	It is placed between the engine and the gearbox in case of automobiles
Answer» C. Torque is transmitted by friction coupling

Discussion

28.	As the number of contacting surface increase in case of the clutch, the torque transmission capacity will:
A.	Decrease
B.	Remain constant
C.	May be increase or decrease
D.	Increase
Answer» E.

Discussion

29.	A trenched conical pivot bearing has semi-cone angle α and the two radii are r1 and r2 respectively with r1 > r2. The coefficient of friction between the sliding surfaces is μ. For an axial thrust load of W kN, the reduction in torque due to friction (assuming uniform rate of wear) is
A.	μW(r1 + r2) cosec α
B.	\(\frac{1}{2}\mu W\left( {{r_1} + {r_2}} \right)\;cosec\;\alpha \)
C.	\(\frac{3}{2}\mu W\left[ {\frac{{{{\left( {{r_1}} \right)}^3} - {{\left( {{r_2}} \right)}^3}}}{3}} \right]cosec\;\alpha \)
D.	\(\frac{2}{3}\mu W\left[ {\frac{{{{\left( {{r_1}} \right)}^3} - {{\left( {{r_2}} \right)}^3}}}{3}} \right]cosec\;\alpha \)
Answer» C. \(\frac{3}{2}\mu W\left[ {\frac{{{{\left( {{r_1}} \right)}^3} - {{\left( {{r_2}} \right)}^3}}}{3}} \right]cosec\;\alpha \)

Discussion

30.	A disk clutch is required to transmit 5 kW at 2000 rpm. The disk has a friction lining with coefficient of friction equal to 0.25. Bore radius of friction lining is equal to 25 mm. Assume uniform contact pressure of 1 MPa. The value of outside radius of the friction lining is:
A.	39.4 mm
B.	49.5 mm
C.	97.9 mm
D.	142.9 mm
Answer» B. 49.5 mm

Discussion

31.	A clutch has to transmit 200 Nm of torque. Assuming uniform pressure theory and the ratio of outer to inner radii is 2.5, what are the radii for a uniform pressure of 2 MPa with the coefficient of friction of the liner material being 0.4?
A.	35 mm and 50 mm
B.	20 mm and 50 mm
C.	35 mm and 80 mm
D.	20 mm and 80 mm
Answer» C. 35 mm and 80 mm

Discussion

32.	Considering the safe design, friction clutch should be designed:
A.	Assuming uniform pressure
B.	Assuming uniform wear
C.	either uniform pressure (or) uniform wear
D.	Uniform pressure for high torque and uniform wear for low torque
Answer» C. either uniform pressure (or) uniform wear

Discussion

33.	In applications like power presses, and rolling mills, where the synchronous operation is required, the most preferred type of clutch is:
A.	Electromagnetic clutch
B.	Positive contact clutch
C.	Friction clutch
D.	Fluid clutch
Answer» C. Friction clutch

Discussion

34.	If the stiffness of a spring of centrifugal clutch is increased, it causes:
A.	decrease of engagement speed
B.	increase of engagement speed
C.	no change in engagement speed
D.	increase the friction torque at maximum speed
Answer» C. no change in engagement speed

Discussion

35.	A clutch has outer and inner diameters 100 mm and 40 mm respectively. Assuming a uniform pressure of 2 MPa and coefficient of friction of liner material 0.4, the torque carrying capacity of the clutch is
A.	148 Nm
B.	196 Nm
C.	372 Nm
D.	490 Nm
Answer» C. 372 Nm

Discussion

36.	A 17-kg ladder has a center of mass at G. If the coefficients of friction at A and B are A = 0.3 and B = 0.2, respectively, determine the smallest horizontal force that the man must exert of the ladder at point C in order to push the ladder forward.
A.	F = 120.2 N
B.	F = 288 N
C.	F = 166.8 N
D.	F = 204 N
Answer» E.

Discussion

37.	The refrigerator has a weight of 200 lb and a center of gravity at G. Determine the force P required to move it. Will the refrigerator tip or slip? Take = 0.4.
A.	P = 75 lb Slips
B.	P = 80 lb Tips
C.	P = 80 lb Slips
D.	P = 75 lb Tips
Answer» E.

Discussion

38.	A uniform beam has a mass of 18 kg and rests on two surfaces at points A and B. Determine the maximum distance x to which the girl can slowly walk up the beam before it begins to slip. The girl has a mass of 50 kg and walks up the beam with a constant velocity.
A.	x = 0.678 m
B.	x = 0.508 m
C.	x = 1.005 m
D.	x = 0.712 m
Answer» D. x = 0.712 m

Discussion

39.	Determine the minimum force F needed to push the two 75-kg cylinders up the incline. The force acts parallel to the plane and the coefficients of friction at the contacting surfaces are A = 0.3, B = 0.25, C = 0.4. Each cylinder has a radius of 150 mm.
A.	F = 919 N
B.	F = 735 N
C.	F = 1.051 kN
D.	F = 981 N
Answer» D. F = 981 N

Discussion

40.	The boy at D has a mass of 50 kg, a center of mass at G, and stands on a plank at the position shown. The plank is pin-supported at A and rests on a post at B. Neglecting the weight of the plank and post, determine the magnitude of force P his friend (?) at E must exert in order to pull out the post. Take B = 0.3 and C = 0.8.
A.	P = 360 N
B.	P = 264 N
C.	P = 229 N
D.	P = 293 N
Answer» C. P = 229 N

Discussion

Explore topic-wise MCQs in Engineering Mechanics.

Sliding friction is _________ than / to rolling friction

Four children were asked to arrange forces due to rolling, static and sliding frictions in a increasing order. Their arrangements are given below. Choose the correct arrangement.

The frictional force exerted by fluids is also called ______

The sole of the shoes becomes plain after wearing it for several months. The reason is

A boat or an aeroplane has a pointed or tapering front / head. Why?

Tyres are treaded to

Spring balance is a device used for measuring the _____________ acting on an object.

Lubricants are substances which

It is difficult to walk on any oily floor because

A matchstick struck on a matchbox catches fire easily because

The value of the frictional force for a body is always constant when it is static and does not vary with applied force.

Consider a block of mass 9.81kg on an inclined surface of the coefficient of friction 0.15 and angle of inclination 30 degrees. What will be its acceleration on the inclined plane if acceleration due to gravity is 9.81 m/s2?

Limiting friction of a body depends on _____

If a box is lying on the floor of a wagon with a coefficient of friction 0.2, what is the maximum acceleration of the wagon for which the box would remain stationary? (Let g = 9.81 m/s2)

_____ is known as the motion that would take place under the applied force if friction were absent.

For a body of mass “m” on a rough inclined plane with a constant but arbitrary coefficient of friction as shown in the figure, what is the angle of repose if the net downward force is donated as “F”. Let “g” be the acceleration due to gravity and “u” be the coefficient of friction.

The maximum value of static friction when the body is at the verge of starting motion is known as _____

What are the types of kinetic friction?

Static coefficient of friction is greater than the kinetic coefficient of friction.

If there are n1 discs on the driving shaft and n2 discs on the driven shaft in a multi-plate clutch, then the number of pairs of contact surface is

A disc clutch is required to transmit 5 kW at 2000 rpm. The disc has a friction lining with the coefficient of friction 0.25. The bore radius of the friction lining is 25 mm. Assume uniform contact pressure of 1 MPa. The value of outside radius of the friction lining in mm is:

In the multiple disc clutch, if there are 6 discs on the driving shaft and 5 discs on the driven shaft, then the number of pairs of contact surfaces will be equal to

A multi-disc clutch employs 3 steel and 2 bronze discs having outer diameter of 300 mm and inner diameter of 175 mm. If the coefficient of friction is 0.25 and axial force on each pair of surfaces is 5 kN, then the torque transmitted (assuming uniform wear) is

In a multiple–disc clutch, the axial intensity of pressure is not to exceed 0.2 MPa. The inner radius of the discs is 100 mm and is half the outer radius. The axial force per pair of contact surfaces in N is

Identify the wrong statement about a single plate clutch from the following.

As the number of contacting surface increase in case of the clutch, the torque transmission capacity will:

A trenched conical pivot bearing has semi-cone angle α and the two radii are r1 and r2 respectively with r1 > r2. The coefficient of friction between the sliding surfaces is μ. For an axial thrust load of W kN, the reduction in torque due to friction (assuming uniform rate of wear) is

A disk clutch is required to transmit 5 kW at 2000 rpm. The disk has a friction lining with coefficient of friction equal to 0.25. Bore radius of friction lining is equal to 25 mm. Assume uniform contact pressure of 1 MPa. The value of outside radius of the friction lining is:

A clutch has to transmit 200 Nm of torque. Assuming uniform pressure theory and the ratio of outer to inner radii is 2.5, what are the radii for a uniform pressure of 2 MPa with the coefficient of friction of the liner material being 0.4?

Considering the safe design, friction clutch should be designed:

In applications like power presses, and rolling mills, where the synchronous operation is required, the most preferred type of clutch is:

If the stiffness of a spring of centrifugal clutch is increased, it causes:

A clutch has outer and inner diameters 100 mm and 40 mm respectively. Assuming a uniform pressure of 2 MPa and coefficient of friction of liner material 0.4, the torque carrying capacity of the clutch is

A 17-kg ladder has a center of mass at G. If the coefficients of friction at A and B are A = 0.3 and B = 0.2, respectively, determine the smallest horizontal force that the man must exert of the ladder at point C in order to push the ladder forward.

The refrigerator has a weight of 200 lb and a center of gravity at G. Determine the force P required to move it. Will the refrigerator tip or slip? Take = 0.4.

A uniform beam has a mass of 18 kg and rests on two surfaces at points A and B. Determine the maximum distance x to which the girl can slowly walk up the beam before it begins to slip. The girl has a mass of 50 kg and walks up the beam with a constant velocity.

Determine the minimum force F needed to push the two 75-kg cylinders up the incline. The force acts parallel to the plane and the coefficients of friction at the contacting surfaces are A = 0.3, B = 0.25, C = 0.4. Each cylinder has a radius of 150 mm.