What is the reading of the spring balance in the following device?

Answer

`40/3 kg`

Explanation

Let T be the reading of the spring balance then
For 20 kg block `20g-T=20a` ….(i)
for 10 kg block `T-10g=10a` …(ii)
Solving Eqs(i) and (ii)
we get `a=g/3 m//s^(2) and T=(40g)/3 N`
So the spring balance reading is `40/3` kg