(a) if th = 1100 k and tc = 400 k, what is the thermal efficiency?

63.6 %

Explanation:

TH = 1100 K , Tc = 400 k

Efficiency is given by

η = 1 - Tc / TH

η = 1 - 400 / 1100

η = 1 - 0.36

η = 0.636

η = 63.6 %

the answer is neither ball has a charge.

because if they were both positively charged, they will repel each other.

if they were positively and negatively charged, they will seek.