Question

Find the reading of the spring balance if $M$ is in equilibrium. Assume all surfaces to be smooth. Take $g=10{\text{m/s}}^2$.

• A. $1kg$
• B. $1.2kg$
• C. $1.4kg$
• D. $1.6kg$

Answer 1

The correct option is B $1.2kg$

The FBDs of the blocks are as shown.


As we know, the spring balance reads the value of spring force $kx$
So, from the FBDs, we have
$N=2.5g\cos {37}^{\circ }$
and, $kx=N\cos {53}^{\circ }=\left(2.5g\cos {37}^{\circ }\right).\cos {53}^{\circ }$
$\Rightarrow kx=2.5\times 10\times \frac{4}{5}\times \frac{3}{5}$
$\Rightarrow kx=12\text{N}$
Thus, the equivalent mass shown by the spring balance is
$\frac{12}{g}=\frac{12}{10}=1.2\text{kg}$