Chapter-04: Turning Effects of Force

After studying this unit, the students will be able to:

• Define like and unlike parallel forces.
• State head to tail rule of vector addition of forces / vectors.
• Describe how a force is resoved into its perpendicular components.
• Determine the magintude and direction of a force from its perpendicular components.
• Define moment of force or torque as moment = force x perpendicular distance from pivot to the line of action of force.
• Explain the turning effect of force by relating it to everyday life. - State the principle of moments.
• Define the centre of mass and centre of gravity of a body.
• Define couple as a pair of forces tending to produce rotation.
• Prove that the couple has the same moments about all points.
• Define equilibrium and classify its types by quoting examples from everyday life.
• State two conditions for equilibrium of a body.
• Solve problems on simple balanced systems when bodies are supported by one pivot only.
• Describe the states of equilibrium and classify them with common examples.
• Explain effect of the position of the centre of mass on the stabililty of simple objects.

1.	If a number of forces act on a body such that their points of action are different but lines of action are parallel to each other then these forces are known as -
	a. Same	b. Parallel
	c. Perpendicular	d. None of above
2.	If the direction of parallel forces is the same, then these are called forces:
	a. Same	b. Like Parallel
	c. Unlike Parallel	d. All of above
3.	If the direction of parallel forces is the opposite, then these are called forces:
	a. Same	b. Like Parallel
	c. Unlike Parallel	d. All of above
4.	Addition of vectors are done by:
	a. Head to tail rule	b. Left hand rule
	c. Right hand rule	d. None of above
5.	Component of a vector acting along the x - axis is called:
	a. x- component	b. horizontal component
	c. vertical component	d. both a and b
6.	component of a vector acting along the y- axis is called:
	a. x- component	b. horizontal component
	c. vertical component	d. both a and b
7.	Value of sin 30°:
	a. 0.5	b. 0.866
	c. 0.707	d. None of above
8.	During rotation the particles of the body rotate along fixed circles. The straight line joining the centres of these circles is known as:
	a. Parallel line	b. Axis of rotation
	c. Both a & b	d. None of above
9.	The rotational effect of a body is measured by a quantity known as:
	a. Acceleration	b. Velocity
	c. Displacement	d. Torque
10.	The rotation produced in a body depends upon ______ factors:
	a. 1	b. 2
	c. 3	d. 4
11.	Torque is a ______ quantity:
	a. Base	b. Vector
	c. Scalar	d. Both a & b
12.	The direction of torque is determined by ______ rule:
	a. Left hand	b. Right hand
	c. Both a & b	d. None of above
13.	If the rotation produced in anti-clock wise direction then the torque is taken as:
	a. Positive	b. Negative
	c. Opposite	d. Perpendicular
14.	If the rotation is produced in clockwise direction then the torque is taken as:
	a. Positive	b. Negative
	c. Opposite	d. Perpendicular
15.	According to right hand rule, if ________ hand then the thumb points in the direction of the torque:
	a. Rotation	b. Parallel
	c. Force	d. Weight
16.	In System International, the unit of torque is:
	a. N	b. Nm-2
	c. Nm-1	d. Nm
17.	The force which is acting perpendicularly downwards towards the earth is called:
	a. Torque	b. Weight
	c. Force of gravity	d. Both b & c
18.	The point at which whole weight of the body appears to act is called:
	a. Origin	b. Couple
	c. Centre of Gravity	d. Reference point
19.	The position of the centre of gravity depends upon the ______ of the body:
	a. Size	b. Shape
	c. Weight	d. Force
20.	The centre of gravity of parallelogram, rectangle, square is the:
	a. Point of intersection of the medians	b. Central point of axis
	c. Point of intersection of the diagonals	d. Centre of parallelogram
21.	The centre of gravity of a regular shaped body is always on its centre of ________:
	a. Body	b. Symmetry
	c. Medians	d. Axis
22.	The centre of gravity of triangle is the:
	a. Point of intersection of the medians	b. Central point of axis
	c. Point of intersection of the diagonals	d. Centre of parallelogram
23.	The centre of gravity of cylinder is the:
	a. Point of intersection of the medians	b. Central point of axis
	c. Point of intersection of the diagonals	d. Centre of parallelogram
24.	When two equal, opposite and parallel forces act at two points of the same body, they form a:
	a. Torque	b. Moment of a couple
	c. Force	d. Couple
25.	A _________ is always acting while opening or closing water tap, a lock, stopper of a bottle or jar:
	a. Couple	b. Weight
	c. Force	d. Mass
26.	The perpendicular distance between the line of action of force and centre of rotation and denoted by ‘r’ is called:
	a. Centre of gravity	b. Moment arm
	c. Displacement	d. Force
27.	The torque produced in a body due to a couple is equal to the product of one of the _________:
	a. Couple	b. Force
	c. Like parallel force	d. Couple arm
28.	There are ______ condition of equilibrium:
	a. 1	b. 2
	c. 3	d. 4
29.	When the sum of all the force acting on a body is zero or the object is moving with uniform velocity then it will be in ________:
	a. Rest	b. Motion
	c. Equilibrium	d. None of above
30.	According to First condition of equilibrium, the sum of all the forces acting on the body should be _______:
	a. Positive	b. Zero
	c. None	d. All of above
31.	According to Second condition of equilibrium, the sum of all the torques acting on the body should be _________:
	a. Positive	b. Zero
	c. None	d. All of above
32.	Sigma () is the Greek letter which is used to represent:
	a. Addition	b. Subtraction
	c. Multiplication	d. Division
33.	There are states of equilibrium:
	a. 1	b. 2
	c. 3	d. 4
34.	The equilibrium in which the body comes back to its original condition when set free after slightly lifting from one side is ______ equilibrium:
	a. Stable	b. Unstable
	c. Neutral	d. None of above
35.	The equilibrium in which the body does not come back to its original condition when set free after slightly lifting from one side is
	a. Stable	b. Unstable
	c. Neutral	d. None of above
36.	The type of equilibrium in which after disturbance, the body again comes to rest position and center of gravity remains unchanged:
	a. Stable	b. Unstable
	c. Neutral	d. None of above
37.	In Stable equilibrium, the centre of gravity is ____ than the original position:
	a. Raised	b. Lowered
	c. Remain same	d. All of above
38.	In Unstable equilibrium, the centre of gravity is ____ than the original position:
	a. Raised	b. Lowered
	c. Remain same	d. All of above
39.	In Neutral equilibrium, the centre of gravity _____ than the original position:
	a. Raised	b. Lowered
	c. Remain same	d. All of above
40.	When an object is resting on the smooth horizontal surface, the w eight of the object is balanced by ________:
	a. Normal Reaction	b. Torque
	c. Friction	d. Couple
41.	A meter rod on a w edge is an example of ______ equilibrium:
	a. Stable	b. Unstable
	c. Neutral	d. None of above
42.	A book lying on the table is an example of ______ equilibrium:
	a. Stable	b. Unstable
	c. Neutral	d. None of above
43.	Motion of the football on the ground is an example of ______ equilibrium:
	a. Stable	b. Unstable
	c. Neutral	d. None of above
44.	The ________ of a racing car is kept low to make its stable:
	a. Width	b. Height
	c. Length	d. Weight
45.	If the centre of gravity of the body is below the fulcrum then the body will be in ________ equilibrium:
	a. Stable	b. Unstable
	c. Neutral	d. None of above

Online Taleem provides students good notes in your study that helps you to quickly review the key points in the material that you have read and clear your concept is an important part of academic success in school / college. It is also an effective learning strategy that intentionally identifying the important content for your desire course and professional practice. This will also help you in improving your comprehension of material and retention.