Question

Two block of mass $8kg$ and $4kg$ are connected by a string as shown. Calculate their acceleration if they are initially at rest on the floor, when a force of $100N$ is applied on the pulley in power direction $(g=10{ms}^2)$

Answer 1

Force applied on the pulley will be 100 N

since pulley is ideal so we can say tension in the string must be 50 N

now we will have

for 4 kg block

$F_t-mg=ma$

plug in all values

50 - 40 = 4a

10 = 4a

$a=2.5m/s^2$

weight of other block of mass 8kg is 80 N

its weight is more than the tension in the string so this block will

remain at rest and its acceleration must be ZERO