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Figure (a) shows two disc  and , rotating about a common axis with constant angular speeds  and ,respectively. Moment of inertia of disc  is  and that of disc  is .The discs are then gently pushed towards each other by forces thatact along the axis. Finally, the discs rub against each other and attain a common angular speed , as shown in figure (b). Match Colums I and II

Column-I

Column- II

(A)

As the discs stick together, the final angular speed,

(p)

Will be zero

(B)

Torque on each disc, due to the force  applied on the disc

(q)

Will be decreasing

(C)

When the discs are rubbing against each other, the kinetic energy of their system

(r)

(D)

Angular momentum of the system

(s)

There will be loss of energy in doing work against the non-conservative internal forces

CODES :

 

A

B

C

D

 

 

a)

B

c

a

 

 

 

b)

c

a

b,d

does notma

 

 

c)

a

c

b

 

 

 

d)

d

a

c

 

 

 



Question ID - 101102 | SaraNextGen Top Answer

Figure (a) shows two disc  and , rotating about a common axis with constant angular speeds  and ,respectively. Moment of inertia of disc  is  and that of disc  is .The discs are then gently pushed towards each other by forces thatact along the axis. Finally, the discs rub against each other and attain a common angular speed , as shown in figure (b). Match Colums I and II

Column-I

Column- II

(A)

As the discs stick together, the final angular speed,

(p)

Will be zero

(B)

Torque on each disc, due to the force  applied on the disc

(q)

Will be decreasing

(C)

When the discs are rubbing against each other, the kinetic energy of their system

(r)

(D)

Angular momentum of the system

(s)

There will be loss of energy in doing work against the non-conservative internal forces

CODES :

 

A

B

C

D

 

 

a)

B

c

a

 

 

 

b)

c

a

b,d

does notma

 

 

c)

a

c

b

 

 

 

d)

d

a

c

 

 

 

1 Answer
127 votes
Answer Key / Explanation : (b) -

(b)

Force  passes through the CM of the discs and hence its torque about CM has to be zero

Also, force of friction will be internal

After the discs stick together, let the final angular speed be

When the discs rub against each other, the kinetic energy will decrease as there will be some loss of energy in doing work against the non-conservative force of friction

Loss of KE

127 votes


127