Question 10: A horizontal force 10 N is applied to a block A as shown in figure. The mass of blocks A and B are 2 kg and 3 kg , respectively. The blocks slide over a frictionless surface. The force exerted by block A on block B is :
(1) zero
(2) 4 N
(3) 6 N
(4) 10 N
Answer: Option (3)
Explanation:
Since the blocks are on a frictionless surface,
both blocks move together with the same acceleration.
The total mass of the system is
m_{\text{total}}=2+3=5\ \mathrm{kg}.
The acceleration of the system is given by Newton’s second law,
a=\frac{F}{m_{\text{total}}}=\frac{10}{5}=2\ \mathrm{m\,s^{-2}}.
The force exerted by block A on block B is the force required to accelerate block B alone.
The mass of block B is 3\ \mathrm{kg}.
Hence, the force on block B is
F_{AB}=m_{B}a=3\times2=6\ \mathrm{N}.
Therefore, the force exerted by block A on block B is 6 N.
Thus, the correct answer is option (3).