IIT JEE , AIEEE Forum - Physics , Mechanics - check ur concepts in rotational mechanics

harsha_27

i hope these questions will truly test ur potential in

rotational mechanics.These qn.s are not created by

me , i've taken these qn.s from a standard book.i'll

post the key on coming sunday (may change

depending on response received).meanwhile u keep

attempting these qns (each member only once plz)

,plz do not try to search for the book from which

i've taken these (i hope Goiitians will not do

that)......strengthen ur concepts and then attempt

these ...ok....1 mark for correct answer and -1 for

wrong answer ,no -ve marks if u don't attempt the

qn., remember post ur answer only once not in bits

ok ..............meanwhile i'll be giving ur

score.........so try out these

true or false questions :

1.A football is placed on a frictionless surface . A

man kicks the football along the ground at the

topmost point.If the same football were to be

placed on ground,which is rough,the football would

move faster.

2.A single force can never make a body rotate.

3.Torque can act only in two directions.It can be

either clockwise or anticlockwise.

4.A body rolls.therefore sliding friction cannot act

on the body.

5.A surface is frictionless.Therefore a body can

never roll on the surface.

6.External torque is acting on a system of bodies .

The angular momentum of this system can never be

conserved.

7.Angular momentum of a system is always

conserved about the hinge or the axis of rotation.

8.A disc has an angular velocity of 2rad/sec..The

moment of inertia about the lowest point is

12Kg-m²(axis passing perp. to plane).Its radius is

2mt..The disc is lying on a flat , horizontal smooth

surface.The angular momentum of the body about

the lowest point is 24kg-m²/sec..

9.The linear momentum of a system is

conserved.Angular momentum will also be conserved

about some point.

10.The mechanical energy of a system is conserved.

Therefore angular momentum will also be conserved

about some point.

11.Two discs(of different sizes) are touching each

other at a point.Both the discs are hinged at the

center.They are rotating with angular velocity as

shown in figure 1 .The common point (pointA of disc

1 and pointA of disc 2)will always have the same

velocity and acceleration.

12.There is a limiting value for maximum velocity

that can be achieved by a disc purely rolling on a

surface irrespective of the external forces acting on

it.

13.A rotating disc is placed on an inclined plane with

friction. There is a maximum angle for the inclined

plane above which the disc will not move up.

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