11. Friction occurs because a. all surfaces have some roughness.
b. surfaces in contact generate heat.
c. chemical reactions take place when surfaces touch.
d. none of the above

electrical potential energy =0.072 j

explanation:

electrical potential energy is given by

u= q δv

q= charge=6 c

δv= potential difference and is given by

δv= e d

e= electric field

d= distance=5 mm=0.005 m

δv=2.4 (0.005)=0.012 v

now electric potential energy= u= q δv

u=6 (0.012)

u=0.072 j

moisture is lackin, and organic acids are scarce.