JEE Advanced 2021 Full Test 2 Paper 1

Let tension in BC & BD be T1 and that in string BA be T2
The string CB and DB make an angle of α=cos−1(

1

√3

) with vertical because the diagonal of a cube makes cos−1(

1

√3

) angle with a side.
Line BM makes β=45° with vertical.
CB=

√3a

2

,CM=

a

2

∴sin‌θ=

1

√3

Resultant of tension in CB and DB is along BM equal to
2T0=2T1‌cos‌θ=2T1√

2

3

Vertical component of T0 balance Mg and its horizontal component is equal to T2.
∴T0‌cos‌β=Mg
T0‌sin‌β=T2
⇒2√

2

3

T1‌sin‌β=T2
⇒2√

2

3

T1

1

√2

=T2
⇒

T2

T1

=

2

√3