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11th Class Chapter 5 Physics Short Questions

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Question: 1
An insect is sitting close to the axis of wheel.If the friction between thw insect and the wheel is very, small, describe the motion of the insect when the wheel starts rotating.
Answer: 1
1-15
When an insect is sitting close to the axis of the friction wheel, and the wheel starts roatation, the insecg will spiral out of the wheel.
Explanaton:
Insect can only remain on its place if it gets sufficient centripetal force. But.
* Friction beween insect and wheel is very small
* Insect cannot get sufficient centripetal force.
Hence insect experiecnes.
* Greater centrifugal force.
* Larger tangential velocity
Therefore;
* Insect slides away from the axis of centre and axis.
* As a result insect will spiral out of the wheel.

Question: 2
Define Centripetal force
Answer: 2
2-15
Centrepetal Acceleration: Acceleratio of circulating body is alwyas direfcted towards the centre is called centripetal acceleration.
Question: 3
Discuss the K.E of the rolling body from an inclined plane.
Answer: 3
3-15
Alternate Text
Question: 4
Is ti possible for a person to distinguish between a raw egg and a hard boiled one by spinning each on a table? Explain.
Answer: 4
4-15
Yes, it is possible to distinguish between a raw egg and a hard-boiled egg through spnning on a tanble
Explanation:
spinning Effect.
Raw Egg Hard boiled egg
The raw egg contains liquid in it. Hard-boiled egg acts as a rigid body
On rotaion the liquid is pushed toward while rotating
outer shell
Moment of inertia of raw egg is greater Moment of inertia of hard
boiled egg is smaller
Question: 5
Why a rifle barrel'rifled'?
Answer: 5
5-15
* Rifiling of barrel gives the spinning motion to a bullet when it's fired.
* Such a design makes trajectory of bullet smooth and more stable as it moves through the air
Explanation:
Rifing of a rifle barrel means cuting spiral or helical grooves on the inner side of the gun barrel
The riffiling of barrel incresses the spin of the bllet about its own axis.
The sping moionof the bullet;
> Helfp the bullet to it along the required direction
> Also stabilizes the bullet, improving its accuracy.
Question: 6
Why is the fly wheel of an engine made heavy in the rim?
Answer: 6
6-15
* The rim of fly wheel of an angine is made heavy to concentrate ore and more mass at perpendiular distance from axis of rotaton.
* This increases moment of inertia
* As result it rotates with uniform rotational speed.
Question: 7
Define Average Angualr Velocity and Intantaneous Angular velocity.
Answer: 7
7-15
Alternate Text
Question: 8
Define Angular Velocity
Answer: 8
8-15
Definiation: The rate of change of angualr displaement is called angualr velocity
Notaion:
It is denoted by w
Question: 9
Alternate Text
Answer: 9
9-15
Alternate Text
Question: 10
Define Angular Displacement
Answer: 10
10-15
Definition: Distance covered in radian 0 by a body moving in circular motion is called angualr displacement.
Angular displacement (radians)= Arc length/radius
SI Unit:
SI unit of angular displacementis radian.
Other Units
Angular displacment is also mdeaured in degrees and revolutions.

Question: 11
Define INstantaneous Angular Acceleration
Answer: 11
11-15
It is defined as rate of change of angular velocity at any instant of time is called instantaneous angualr acceleation.
Question: 12
At what speed is a bank angle of 45 o requied for an aertoplane to turn 60 m?
Answer: 12
12-15
Alternate Text
Question: 13
Why does the coasting rotating ystem slow down as water drops into the beaker?
Answer: 13
13-15
The coasting rotating system slows down because of the increse in moment of inertia of the beaker.
Explanation:
According to thelaw of conservation of angular momentum.
L= 1 w = constnat
w= constant/l
w inversal proportion 1/l
When the water is put into the beaker,
The mass of the beaker increases
As a result moment of inertia will increases becassue l = mr2
Therefore to conserve angular momentum its angular velocity will decrease.
Question: 14
When a tractor moves with uniform velocity its heavier wheel rotates slowly than its lighter wheel, why?Explain.
Answer: 14
14-15
When a tractor moves with uniform velocity its heavier wheel rotates slowly than its lighter wheel, due to the differene in.
* The radius of the both the wheels.
* As a result difference in moment of inertia.
Explanation: If the radius of heavier wheel is r1 then distance covered by it is;
S1 = rotations per second x r1
If the radius of lighter wheel is r2 then distance covered by it is;
S2 = rotations per second x r2
As both wheels are attached to same tractor therefore they cover equal distance in equal time .i.e.
S1 = S2
rotations per second x r1 = rotations per second x r2
Since r2> r2 therefore heavier wheel must less number of rotations per second in same time to cover same distance . Hence it moves slowly.

Question: 15
Explain the significance of moment of insertia in rotatory motion.
Answer: 15
15-15
Momen of inertia is the tenency to oppose any change in the rotational motion by a body.
Explanation:
From Newton's 2nd law.
F = ma........................ eq.1
Torque in angular motion is written as;
Torque= la............................ eq2
By comparing eq.1 and eq .2 it is clear that
* The moment of inertia 'l' performs the same role in rotational motion as mass plays in translational motion.
* Hencw the significance of moment of inertia is to oppose any change in the rotational motionof a body.

11th Class Physics Chapters Short Questions