What are the differences between u brakes and v brakes, and which one is more effective for stopping power?

U brakes and V brakes are two types of bicycle brakes that differ in their shape and design. V brakes have arms that form a "V" shape, while U brakes have a more curved shape resembling the letter "U." In terms of stopping power, V brakes are generally considered more effective due to their greater leverage and ability to apply more force to the wheel rim.