Which one of the following front suspension systems is not used on passenger cars but is used on some trucks?

The I-beam front suspension system is often associated with heavy-duty trucks and certain larger vehicles rather than passenger cars. This design provides the necessary strength and stability required for trucks that carry heavier loads, making it particularly suitable for commercial and utility applications. The I-beam is a solid beam that runs across the vehicle's front end, contributing to the vehicle's ability to handle heavy stress and maintain structural integrity under load.

In contrast, the other options, such as McPherson struts, torsion bars, and ball joints, are commonly found in passenger cars due to their ability to provide better ride quality, handling characteristics, and ease of manufacturing suited for lighter vehicles. These systems focus on offering a balance of comfort and performance, which is essential for passenger vehicles.