Answer:
12.5 N
Explanation:
We can find out about the tension of the cord pulling the 5kg mass by first calculate the horizontal acceleration of said mass, which is the same as the horizontal acceleration of the whole system.
Total system mass M = 5 + 7 = 12 kg
Total system acceleration = F/M = 30/12 = 2.5 (m/s2)
The tension force acting on the 5kg mass in order to exert a 2.5 m/s2 acceleration is
f = ma = 5*2.5 = 12.5 N
