Physics - NLM Question with Solution | TestHub

Maximum friction between the blocks: $f_{max}=\mu mg=0.5\times 5\times 10=25$N

Actual friction is 20 N $<25$N, so the blocks move together

Friction drives the 10 kg block: $a=20/10=2$m/s ${}^2$

For the system: $F=(5+10)\times 2=30$N