Hot water pipes are painted black why?

Absorb heat

Explanation:

Hot water are painted black so as to absorb more heat and since black surfaces have low emission levels (emissivity), pipes painted black would retain hot water longer than normal pipes.

In essence, hot water pipes are painted black because of it's high absorption (good absorber of heat) and low emission of heat. Hence it prevents lose of heat within the pipes much better than regular pipes.

at positions a, g kinetic energy is maximum.

at position d, potential energy is maximum.

0.11 m/s and 0.28 m/s should be correct