Well, let's work off of your 50 pound object. How do you want to move this 50 pound object? are you going to be sliding it across the floor, using a cable? Are you going to be lifting this 50 pound object up off of the floor?
Are you going to be using the motor as a drive motor for some sort of 50 pound vehicle? The reason that I am asking? The application is important to consider, especially when calculating the type of motor that you need. Lifting an object involves differently vectored forces when compared to driving an object with a motor, thus, we need to consider what forces will be working against the motor. Then we can effectively approximate the torque, RPMs, and power requirements for the motor.