JEE Main Physics Class 11 Work, Energy and Power Part 1 Questions

Initial momentum of the system block (C) =mv0. After striking with A, the block C comes to rest and now both block A and B moves with velocity v when compression in spring is x0.
By the law of conservation of linear momentum
mv0=(m+2m)v⇒v=

v0

3

By the law of conservation of energy
K.E. of block C=K.E. of system + P.E. of system

1

2

mv02=

1

2

(3m)(

v0

3

)2+

1

2

kx02
⇒

1

2

mv02=

1

6

mv02+

1

2

kx02
⇒

1

2

kx02=

1

2

mv02−

1

6

mv02 =

mv02

3

∴k=

2

3

m(

v0

x0

)2