Question

Two blocks of masses $m_1=4kg$ and $m_2=6kg$ are connected by a string of negligible mass passing over a frictionless pulley as shown in the figure. The coefficient of friction between block $m_1$ and the horizontal surface is 0.4. When the system is released, the masses $m_{1}and{m}_2$ start accelerating. What additional mass $m$ should be placed over mass $m_1$ so that the masses $(m_1+m)$ slide with a uniform speed?

• A. 9 kg
• B. 10 kg
• C. 11 kg
• D. 12 kg

Answer 1

The correct option is C

11 kg

For the system to move with a uniform speed, net force on each block should be zero.
$T=m_{2}g$
Also, $T=f=\mu (m_1+m)g\Rightarrow m_{2}g=\mu (m_1+m)g\Rightarrow m_2=\mu (m_1+m)\Rightarrow 6=0.4(4+m)\Rightarrow m=11kg$
Hence, the correct choice is (c).