TyroCity: Physics XI Notes

How will you make difference between density and specific gravity of a body?

Physics XI Notes — Sun, 18 Aug 2013 05:41:42 +0000

Density	Specific gravity
The density of the substance is defined as the mass per unit volume of that substance.	Specific gravity of a substance is defined as the ratio of the mass of certain volume of it to the mass of the same volume of water at 4ËšC.
Its unit is kg/m³ or g/c.c.	It has no unit because it is the ratio of same physical quantity.

Distinguish between conservative and non-conservative force.

Physics XI Notes — Sun, 18 Aug 2013 05:41:42 +0000

Conservative force	Non-conservative force
A force is said to be conservative if the work done by or against force is dependent only on the initial and the final position of the body and not on the path followed by the body.	A force is said to be non-conservative if the work done by or against the force is dependent on the path followed by the body.
Work done by the conservative force in a closed path is zero.	Work done by the non-conservative force in a closed path is not zero.
Eg: Gravitational force, magnetic force, electrostatic force, etc	Eg: friction, viscous force, induction force in cyclotron, etc.

Explain why spokes are fitted in the cycle wheel.

Physics XI Notes — Sun, 18 Aug 2013 05:41:42 +0000

The spokes of cycle wheel increases its moment of inertia. The greater the moment of inertia, the more is the opposition to any change in uniform rotational motion. As a result cycle runs smoothly and steadily. Of the cycle wheels had no spokes, the cycle would be driven jerky and hence unsafe.

Thermal Properties of Matter- Old is Gold

Physics XI Notes — Sun, 18 Aug 2013 05:41:42 +0000

Which has more atoms: a kilogram of hydrogen or a kilogram of iron?
Molecules of different gases have equal average kinetic energies, provided their temperature is the same. Do these molecules have equal velocities also?
Outline the essential features of the kinetic theory of gases.
Why do you consider an ideal gas while formulating the pressure in the light of kinetic theory of gases?
Why does the cycle tube burst sometimes in summer?
At absolute zero temperature, why the kinetic energy is zero?
Under what conditions do the real gases obey more strictly the gas equation PV=RT?
Write the unit of the universal gas constant and give its physical meaning.
In the kinetic theory of gases, why do we not take into account the changes in gravitational potential energy of the molecule?
Absolute zero temperature is not zero energy temperature. Explain.
What are the characteristics of a gas to be an ideal?

Viscosity-Old is Gold

Physics XI Notes — Sun, 18 Aug 2013 05:41:42 +0000

Machine parts are jammed in cold days. Why?
During certain windstorm, light roofs are blown off, why?
Define viscosity. Does it depend on temperature?
When a smooth-flowing stream of water comes out of a faucet, it narrows as it falls. Explain why this happens.
Explain why a suction effect is experienced by a person standing close to the platform at a station when a fast train passes.
Why does a flag flutter on strong wind?

The weight of a body is less inside the earth than on the surface. Explain.

Physics XI Notes — Sun, 18 Aug 2013 05:41:42 +0000

We have,

As we go inside the earth, the value of ‘x’ increases as a result the value of ‘g’ decreases. Therefore, the weight of the body is less inside the earth than on the surface.

Work

Physics XI Notes — Sun, 18 Aug 2013 05:41:42 +0000

Work is said to be done if a force displaces any object in any direction other than 90˚ to the direction of force applied.
If ‘F’ be the force applied and ‘d’ be the displacement and ‘θ’ be the angle between ‘F’ and ‘d’, work done by the force is,
W = Fcosθd
= Fdcosθ
W= F.d
Work is a scalar quantity. Its SI unit is Joule.

a) When the angle between F and d is acute, the work done by the force is positive.
Eg:- Pushing a duster moves the duster in the direction of force. So θ=0˚ then,
W = Fdcosθ
= Fcos0˚
= Fd [Work is positive]

b) When the angle between F and d is 90˚, the work done is zero.
Eg:- A coolie carry a load and walking on horizontal road does no work because the direction of force is vertical while he moves in horizontal direction. So,
W = Fdcos90˚
= 0

c) When the angle between F and d is 90˚<θ≤180˚, then work done is negative.
Eg:- When a body is pushed, it moves in the direction of force. Work done by the force is positive but the work done by friction is negative.
W = Frdcos180˚
= -Frd

Explain why a coin placed on a cardboard covering a glass falls into the glass when the cardboard is pulled to one side?

Physics XI Notes — Sun, 18 Aug 2013 05:41:42 +0000

Explain why a coin placed on a cardboard covering a glass falls into the glass when the cardboard is pulled suddenly to one side

Ans: Due to inertia of rest, the coin tends to be at rest.

What will happen to the value of ‘g’ if the earth stops rotating?

Physics XI Notes — Sun, 18 Aug 2013 05:41:42 +0000

Variation of ‘g’ due to rotation is given by
g = g’ – ω2R
If earth stops rotating then ω=0 then

g = g’- 0 = g’

Therefore, the value of ‘g’ increases if the earth stops rotating.

Why is a horse more stable than a man?

Physics XI Notes — Sun, 18 Aug 2013 05:41:42 +0000

The C.G. of the horse is lowered to the base of the body and the base of the foot is greater than the man, so the horse is more stable than the man.

Explain why the moon has no atmosphere?

Physics XI Notes — Sun, 18 Aug 2013 05:41:42 +0000

Moon has no atmosphere because the value of acceleration due to gravity ‘g’ on the surface of moon is small. Therefore, the value of escape velocity on the surface of moon is small. The value of r.m.s. velocity of the molecules of different gases is much above the value of escape velocity on moon. That is why all the molecules of gases escaped and there is no atmosphere on moon.

Kinematics-Old is Gold

Physics XI Notes — Sun, 18 Aug 2013 05:41:42 +0000

Because of air resistance, two objects of unequal mass do not fall at precisely the same rate. If two bodies of identical shape but unequal mass be dropped simultaneously from the same height, which one reaches the ground first?
Can an object with constant acceleration reverse its direction? Explain.
If the displacement of a body is proportional to square of time, state the nature of motion of the body.