The cable of a hoist has a cross-section of 80 mm2. The hoist is used to lift a crate weighing 500 kg. What is the stress in the cable? The free length of the cable is 3m. How much will it extend if it is made of steel (modulus 200 GPa)? How much if it is made of polypropylene, PP (modulus 1.2 GPa)?