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# 9th Class Chapter 4 Physics Long Questions

Dear students, prepare for physics class 9th chapter 4 long questions. These important long questions are carefully added to get you best preparation for your 9th class physics ch. 4 exams. ### 0

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##### Question: 1
Q no: 5 (A) What is meant by torque or moment of a force<gwmw class="ginger-module-highlighter-mistake-type-6" id="gwmw-15858262083335148330822"> ?</gwmw> Explain the factors on which it <gwmw class="ginger-module-highlighter-mistake-type-3" id="gwmw-15858261827338929261950">depend</gwmw>
1-19
The rotational effect of a force is measured by a quantity know as torque
Dependence of torque:
Rotation produced in a body depends on the following two factors
1-force
2 Moment Arm

Force:
Greater is the force; greater is the moment of the force
Line of action of force:
The line along which a force acts is called the line of action of force.
Moment Arm:
The perpendicular distance between the line of the force and the axis of rotation is as moment arm. Longer is the moment arm greater is the moment of force.
Mathematicle form:
Torque = Moment arm x Force
torque = F x l
Unit:
The unit of toque is Newton meter (Nm)
##### Question: 2
A mechanic tightens the nut of a bicycle using a 15 cm long <gwmw class="ginger-module-highlighter-mistake-type-1" id="gwmw-15858270386888255705007">spanner</gwmw>by exerting a force of 200 N. Find the torque has tightened it.
2-19
Solutions:
F= 200N
L= 15cm = 0.15m
t= ?
t= F x L
t = 200 x 0.15
t =30Nm Ans
##### Question: 3
Q no<gwmw class="ginger-module-highlighter-mistake-type-6" id="gwmw-15858276955347944999763"> :</gwmw>6<gwmw class="ginger-module-highlighter-mistake-type-6" id="gwmw-15858276955348863652694">(</gwmw>a) What is meant by <gwmw class="ginger-module-highlighter-mistake-type-3" id="gwmw-15858276955340132629638">principle</gwmw> of moments? Explain clockwise torque and anticlockwise torque.
3-19
Principle of Moments:
A body is balanced if the sum of clockwise moments acting on the body is equal to the sum of anticlockwise moments acting on it
Explanation:
A force that turns a spanner in the clockwise direction is generally used to tighten a nut. The torque or moment of the force so produced is called Clockwise moment. On the other hand to loosen a nut, the force is applied such that it turns the nut , the force is applied such that it turns the nut, the force is applied such that it turns the nut in the anticlockwise direction. The torque or moment of the force so produced is called anticlockwise direction. The torque or moment of the force so produced is called anticlockwise moment.
##### Question: 4
Q no<gwmw class="ginger-module-highlighter-mistake-type-6" id="gwmw-15858320060491154138267">:</gwmw>6<gwmw class="ginger-module-highlighter-mistake-type-6" id="gwmw-15858320060497974131645">(</gwmw>B) The steering of a has a radius 16 cm. Find the torque produced by a couple of 50 N.
4-19
F = 50 N
r= 16 cm
d= AB = 32cm =0.32m
t=?
As we know that
t = Fx AB
t = 50 x 0.32
t = 16Nm
##### Question: 5
Q no: 7<gwmw class="ginger-module-highlighter-mistake-type-6" id="gwmw-15858348374198525100282">(</gwmw>A) Define parallel forces. Also explain its types or what is the difference between Like and Unlike parallel forces?
5-19
We often come accrossobjects on which many forces are acting.
In many cases, we find all or some of the forces acting on a body in the same of the forces actinf on a body in the same direction for example, many people push a bus it in the. Why all of them push it in the same direction? All these forces are applied in the same direction so these are all parallel to each other. Such forces which are parallel to each other are called parallel forces
Types:
There are two types of parallel forces
1- Like parallel force
2- Unlike parallel force

1- Like parallel forces:
Like parallel forces are those forces that are parallel to each other and have the same direction

2- Unlike Parallel forces:
Unlike parallel forces are the forces that are parallel but have directions opposite to each other.
##### Question: 6
Q no: 7 (B) A force is acting on a body making an angle of 30 with the horizontal. The horizontal component of the forceis 20 N. Find the force.
6-19
Solution:
=20 N
Q = 30°
F = ?
As we know that
Fx= F cosθ
F = Fx/Cosθ
F = 20/cos30°
F = 20//o.866
F = 23.09N
F= 23.1 N
##### Question: 7
Explain like parallel and unlike parallel forces
7-19
Parallel forces: such forces which are parallel to each other are called parallel forces.ORthe forces which can never cross 3each other a re called parallel forces.Example: we often come across objects on which many forces are acting in many cases, we find some or all forces acting on the body in the same direction e.g. many people push a bus to start it, all the people apply the forces in the same direction so thy are called parallel forces.
##### Question: 8
8-19
Addition of forces: force is a vector quantity. it has both magitude and direction; therre fore , forces are not added b ordinary arithmetical rules. when forces are added, we get a resultant force.
##### Question: 9
Discuss resolution of forces
9-19
To split up a force into its perpendicular components is called resolution of the force.
##### Question: 10
Discuss torque or moment of force
10-19
Before discussing torque we need some terms to define first.Rigid body: a body is composed of large numbver of small particles. If the distance between all paisrs of particles of the body do not change by applting all pairs of particles of the body don not change by applying a force . then it is called a righid bodyAxis of rotation: when a rigid body rotate s its particles also rottate in specific circle. The line joininig the centres of therse circles is called axis of rotatioinORThe line passes through the body and body can rotate aroun it. This line is called axis of rotation
##### Question: 11
Explain principle of moments
11-19
Principle of moment: a body is balanced if the sum o clockwise moments acting on the body is equal to the sum of anticlockwise moments acting on it.There are two types of momentsClockwise moment, anticlockwise moment
##### Question: 12
Define center of mass and explain it with the help of example
12-19
Centre of mas: center of mass of a system is a point where an applied force causes the system to move without rotationExplanation: it is observed that the center of mass of system moves as if its entire mass is confined at that points, the force acting on this point will not produce torque.
##### Question: 13
What is center of gravity. also explain it
13-19
Centre of gravity: a point where the whole weight of the body appears to act vertically downward is called center of gravityExplanation: a body is made of large number of particles. Earth attracts all particles vertically downward. Ass the weight is a vector quantity, the resultant of all these parallel forces is a single force equal to the weight of the whole body. A point where this resultant force acts vertically towards the center of earth is called center of gravity
##### Question: 14
How we determine the center of gravity of an irregular shaped thin lamina
14-19
Center of gravity of an irregular shaped thin lamina: a simple method to find center of gravity of an object is by the use of a plumb linePlumb line: a plumb line consists of a small metal bob supported by a string. When the bob is suspended freely by the truing. Its weight acts vertically downward. In this state, center of gravity of the bob is exactly below its point of suspension
##### Question: 15
Define couple and explain it mathematically
15-19
Couple: a couple is formed by two unlike parallel forces of same magnitude but not along the same lineExample: two unlike forces act on a steering wheel and produce torque to turn the vehicle. Similarly, a double arm spanner is used to open a nut of the tyre . Two equal and unlike forces on a water tap produce torque hence , they act as a couple.
##### Question: 16
State and explain mathematically first condition for equilibrium
16-19
First condition of equilibrium: a body is said to satisfy first condition of equilibrium if the resultant of all the forces acting on it zeroForces can act in two waysHorizontally, Vertically
##### Question: 17
state and explain second condition for equilibrium.
17-19
Second condition for equilibrium: if the sum of all the torques acting on a body is zero then the body is in state of equilibrium
##### Question: 18
Write and explain the states of equilibrium