A female worker in the workplace has a safe limit to lift objects weighing 160 N (16 kg) at places of work. The worker can lift weights greater than 160 N using a trolley. You may consider a 1.5 m long trolley, weighing 100 N, and the center of gravity located at 0.6 m from the axle. Assume the load's center of mass is located 0.6 m from the axle. What is the source of the force that enables the worker to lift more weight using the trolley?