Question

Two blocks of masses 7 kg and 5 kg are placed in contact with each other on a smooth surface. lf a force of 6 N is applied on the heavier mass, the force on the lighter mass is

• A. 3.5 N
• B. 2.5 N
• C. 7 N
• D. 5 N

Answer 1

Answer: (B)

2.5 N

Answer 2

Since, surface is smooth, therefore both the blocks move with same acceleration (say a).
Common acceleration.
$\, \, \, \, \, \, \, \, \, \, a = \frac{F}{M + m}$
$= \, \, \, \, \, \, \, \, \frac{6}{7 + 5} = \frac{1}{2} ms^{-2}$
Therefore, force on lighter mass
$\, \, \, \, \, \, \, \, \, \, \, \,$ F' = ma
$\, \, \, \, \, \, \, \, \, \, \, = 5 \times \frac{1}{2} = 2.5 N$