Question

Two blocks A and B of masses 10 kg and 15 kg are placed in contact with each other rest on a rough horizontal surface as shown in the figure. The coefficient of friction between the blocks and surface is 0.2. A horizontal force of 200 N is applied to block A. The acceleration of the system is :

(Take $g = 10ms^{- 2}$)

• A. $4ms^{- 2}$
• B. $6ms^{- 2}$
• C. $8ms^{- 2}$
• D. $10ms^{- 2}$

Answer 1

Answer: (B)

$6ms^{- 2}$

Answer 2

Here Mass of block A,

$m_{A} = 10kg$

Mass of block B, $m_{B} = 15kg$

Coefficient of friction between the blocks and the surface, $\mu = 0.2$

Applied force =200N

Force of friction on

$A = \mu N_{A} = \mu m_{A}g = 0.2 \times 10 \times 10 = 20N$

Force of friction on

$B = \mu N_{B} = \mu m_{B}g = 0.2 \times 15 \times 10 = 30N$

Taking two blocks forming one system, therefore net force acting on the blocks is

$F = 200 - 20 - 30 = 150N$

Let a be common acceleration of the system

$\therefore a = \frac{F}{m_{A} + m_{B}} = \frac{150N}{(10 + 15)kg} = 6ms^{- 2}$