Advantages of copper cables are that copper is an extremely powerful conductor of electricity and much more stable over time. It can withstand higher temperatures than aluminum and is more resistant to damage.
Disadvantages: Copper is more expensive and heavier and thus requires structural support.
Advantages of aluminum cables are that it is less expensive, easier to work with and light weight and so does not need structural support when strung over long distance.
Disadvantages: Aluminum is more susceptible to corrosion and requires periodic replacement. It needs much greater maintenance.
Advantages of steel cables are that steel does not rust, is fairly cheap and readily available. It has a higher tensile strength too.
Disadvantages: Steel cables are less ductile and are therefore more susceptible to fatigue.
The weight of an object on Earth is equal to W=9.81M where M is the mass of the object and the acceleration due to gravity is 9.81 m/s^2. Therefore, the weight of the book on the earth is W=9.81(2.2)=21.582N, or 21.582 Newtons
