Question

Two masses as shown are suspended from a massless pulley. Calculate the acceleration of the 10 kg mass when masses are left free

• A. $\frac{2g}{3}$
• B. $\frac{g}{3}$
• C. $\frac{g}{9}$
• D. $\frac{g}{7}$

Answer 1

The correct option is B $\frac{g}{3}$

As the string and pulley system is ideal so the tension will be $constant$ throughout the string and thus both blocks

will move with same acceleration in magnitude, suppose the tension is $T$ and the common acceleration is $a$

The $10kg$ being heavy will move $downward$.

$Note-$

Tension always act towards a direction $away$ from the block.

net $Downward$ force on $10kg$ block will be $10g-T$

so the equation of Force will be $F=ma$ or $10g-T=10a$ ............(1)

Similarly net $upward$ force on $5kg$ block will be $T-5g$

so the equation of Force will be $F=ma$ or $T-5g=5a$ ............(2)

adding equation-1 and 2 we get $5g=15a$

or $a=\frac{g}{3}$