Question

Two blocks of masses $2kg$ and $5kg$ are at rest on the ground. The masses are connected by a string passing over a frictionless pulley which is under the influence of a constant upward force $F=50kgm/s^2$. The accelerations of $5kg$ and $2kg$ masses are :

• A. $0,2.5{ms}^{-2}$
• B. $0,0$
• C. $2.5{ms}^{-2},2.5{ms}^{-2}$
• D. $1{ms}^{-2},2.5{ms}^{-2}$

Answer 1

The correct option is A $0,2.5{ms}^{-2}$

Here the masses will be lifted if the tension in the sting is greater than the gravitational pull of the masses.
Weight of $2kg$ mass $=2g=20N$
Weight of $5kg$ mass $=5g=50N$
From FBD, $2T=50\Rightarrow T=25N$
As the weight of $5kg$ mass is less than the tension. so it can not lift and its acceleration is zero.
Now for $2kg$ mass, $2a=25-20=5\Rightarrow a=2.5m/s^2$