Workers load a 500kg safe onto an elevator that lifts it 90m to the twentieth floor of a building. how much work did the elevator do on the safe?

Work is Force X Distance. The force is equal to mass X acceleration (F=MA). In this case the acceleration is gravity, which is 9.81 m/s^2. So you multiply 500 by 9.81 to get 4905 Newtons (N). This is the amount of force required to lift the safe. Multiply this force by the distance, which in this case is 90 meters. This gives you 441450 Newton Meters (N*m) of work. 1 N*m is equivalent to 1 Joule (J), so the answer can be written as 441450 Joules (J).