9th Class Chapter 4 Physics Long Questions

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.

Solutions:

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.

Principle of Moments:

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.

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?

We often come accrossobjects on which many forces are acting.

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.

Solution:

Explain like parallel and unlike parallel forces

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.

Discuss briefly addition of forces

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.

Discuss resolution of forces

To split up a force into its perpendicular components is called resolution of the force.

Discuss torque or moment of force

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

Explain principle of moments

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

Define center of mass and explain it with the help of example

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.

What is center of gravity. also explain it

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

How we determine the center of gravity of an irregular shaped thin lamina

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

Define couple and explain it mathematically

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.

State and explain mathematically first condition for equilibrium

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

state and explain second condition for equilibrium.

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

Write and explain the states of equilibrium

States of equilibrium: there are three states of equilibriumStable equilibrium ,Unstable equilibrium, Neutral equilibrium

How position of center of mass effects stability

center of mass helps in stability. T make the object stable, center of mass is kept as low as possibleExample: Racing cars are made heavy at the bottom and height is kept as low as possible.Circular artist such as tight rope walker use long poles to lower their center of mass.In above two examples low center of mass helps them to prevent from topple over