IIT JEE , AIEEE Forum - Physics , Mechanics - friction... a B.MAT question....proper solution required.......

sharmadon

two blocks of masses m_a=2kg and m_b=4kg are kept on an inclined plane of inclination

= 37degree as shown.The coefficient of friction bw A and B is

₁ and bw B and surface is

₂. accelerations of blocks A and B are a₁ and a₂. then match the following.

column I column II

1.a₁=a₂A.₁= 0.3 and

₂ = 0

2.a₁

a₂ B ₁= 0.8 and

₂ = 0.8

3.if work done by friction on block B is zero,then C.₁= 0 and

₂ = 0.2

4.if net contact force on block A is normal force,then D.₁= 0.4 and

₂ = 0.8

ganesha1991

since they have common acceleration
they can be considered as a system
now for the system of A&B
mgsin37 -

₂ mgcos37 = ma
gsin37 -

₂ gcos37 = a
simplifying we get
6 - 8

₂ = a ---------------------(1)

now for block A
mgsin37 +

₁ mgcos37 - ma (pseudo force)= 0
gsin37 +

₁ gcos37 = a
simplifying we get
a = 6 + 8

₁ --------------------------(2)
from 1 and 2
6+8

₁ = 6 - 8

₂
or

₁ = -

₂

therefore it is option B

correct me if i"m wrong

ganesha1991

i think 3 is A and C

₁ mgs = 0

₁ =0
case 2

₂ mgs = 0

₂ =0

therefore it is A and C

anchitsaini

what i think is that since u have said a1 = a2 only when option B is correct
hence
a1 ! = a2 when option a,c,d are correct

sharmadon

hey the answrs according to the solution given by Brilliant tutorials is:

1. A,B

2. C,D

3. A,B,D

4. A,C

and my friend ganesha..u can consider it as a system only wen u can confirm that they move together..please justify...

i am really very tensed about such kind of questions..pls somebody help........with proper solution..

vidyarthi

http://www.locuseducation.org/component/option,com_fireboard/Itemid,26/func,view/catid,10/id,524/#524

gaurav3sharma

THE FIRST PART..

gaurav3sharma

SECOND AND THIRD PART..

gaurav3sharma

FOURTH PART..

ganesha1991

ok for the first one A is correect
as there is no friction between the wedge and block B the whole A and B can be considered as one system with common acceleration

so from my present and previous post
the answer for 1 is
A) and B)

ganesha1991

since a1 is not equal to a2 the other two options must be true fior this
therefore for 2 answer is
C) , D)

[ thanks anchit]

vidyarthi

http://www.locuseducation.org/component/option,com_fireboard/Itemid,26/func,view/catid,10/id,528/#528

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