Question

2. Two blocks of masses m, and m, are placed side by side on a smooth horizontal surface as shown in
the figure. A horizontal force Fis applied on the block my.
What will happen after applying the force?
​

Answer 1

Answer:

Method 1 :

Since the two blocks always remain in contact with each other, they must move with the same acceleration. Using Newton's second law, we get

For block m

1

:F−N=m

1

a......(i)

For block m

2

:N=m

2

a......(ii)

On adding the two equations, we get

F=(m

1

+m

2

)a⇒a=

m

1

+m

2

F

Substituting the value of a in (ii), we get N=m

2

a=

m

1

+m

2

Fm

2

Method 2 :

The situation may be considered as follows: Instead of drawing the free-body diagrams of each block, we can draw the free-body diagram of both blocks together as shown in Fig.6.33.

The net force acting on the system is F, and the total mass of the system is

m

1

+m

2

. Thus, a=

m

1

+m

2

F

To find out the normal reaction N between the two blocks, we can imagine the following; Block m

2

is moving with an acceleration a; therefore, the net force acting on it must be m

2

a, which is nothing but the normal reaction applied by the block m

1

. Thus,

N=m

2

a=

m

1

+m

2

m

2

F