Which is true for rolling frictrion 

Subject

Physics

Class

NEET Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

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1.

Which is true for rolling frictrion   μr , static friction μs  and  kinetic friction  μk :

  • μs > μk >  μr

  • μs <  μk <  μr

  • μs <  μk >  μr

  • μs > μr  > μk


A.

μs > μk >  μr

Static friction is a force that keeps an object at rest. It must be overcome to start moving the object. When external force exceeds the maximum limit of static friction body begins to move.
 
Once the body is in motion it is subjected to sliding or kinetic friction which opposes relative motion between the two surfaces in contact. At every instant, there is just one point of contact
between the body and the plane and this point has no motion relative to the plane. In this ideal situation, kinetic or static friction is zero and the body should continue to roll with constant velocity. 
In practice, this will not happen and some resistance to motion (rolling friction) does occur, i.e. to keep the body rolling. Static friction is always greater than kinetic friction and rolling friction is less than kinetic friction.
                        μs >  μk > μr

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2.

Two weights w1 and w2 are suspended to the two strings on a frictionless pulley. When the pulley is pulled up with an acceleration g, then the tension in the string is :


3.

Two similar charges having mass m and 2m are placed in an electric field. The ratio of their kinetic energy is :

  • 4:1

  • 1:1

  • 2:1

  • 1:2


4.

In a system of units if force (F), acceleration (A), and time (T) are taken as fundamental units, then the dimensional formula of energy is:

  • FA2T

  • FAT2

  • F2AT

  • FAT


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5.

A car starts from rest, moves with an acceleration a and then decelerates at a constant rate b for sometimes to come to rest. If the total time taken is t. The maximum velocity of car is given by :

  • a b ta + b 

  • a2 ta + b

  • a ta+ b

  • b2 ta+b


6.

Two planets are revolving around the earth with velocities v1 and v2 and in radii r1 and r2 ( r1 > r2 ) respectively. Then :

  • v1 = v2

  • v1 > v2

  • v1 < v2

  • v1r1 =v2r2


7.

The angular momentum of a rotating body changes from Ao to 4Ao in 4 minutes. The torque acting on the body is:

  • 3/4 Ao

  • 4Ao

  • 3Ao

  • 3/2Ao


8.

Earth is revolving around the sun. If the distance of the earth from the sun is reduced to 1/4th of the present distance then the length of present day will be reduced by :

  • 14

  • 12

  • 18

  • 16


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9.

There are two planets and the ratio of radius of the two planets is K but ratio of acceleration due to gravity of both planets is g. What will be the ratio of their escape velocity ?

  • (kg)1/2

  • (kg)-1/2

  • (kg)2

  • (kg)-2


10.

If a spherical ball rolls on a table without slipping the friction of its total energy associated with rotational energy is :

  • 3/5

  • 2/7

  • 2/5

  • 3/7


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