A person's heart and head are 1.3 m and 1.8 m above the feet, respectively. Determine the potential energy associated with 0.5 kg of blood in the heart relative to (a) the feet, (b) the head. 15. A toy gun uses a spring to project a 5.3 g soft rubber sphere horizontally. The spring constant is 8.0 N/m, the barrel of the gun is 15 em long, and a constant frictional force of 0.032 N exists between barrel and projectile. With what speed does the projectile leave the barrel if the spring was compressed 5.0 em for this launch?