Question

The blocks are attached by an in extensible light string and pulled vertically upward by force 100 N as shown. Find the common acceleration and tension the string.

Answer 1

Taking two blocks and string as system

(i) $F_y=m{a}_y$ Ref. image

$F-49-2g=(4+2)a$

$=120-40-20=6a$ or $6a=60$

$a=10m/s^2$

Ref. image

(b) $T-2g=2a$

$T-20=\left(2\right)\left(10\right)$

$\therefore$ $T=40N$