A spring is fixed at one end and is compressed by applying a force to the other end. The variation of the force F acting on the spring with its compression x is shown in Fig. 3.1. [Figure 3.1] A compression of 0.045m is produced when a force F₁ acts on the spring. The spring has a spring constant of 800 Nm⁻¹. A child's toy uses the spring in (a) to launch a ball of mass 0.020 kg vertically into the air. The ball is initially held against one end of the spring which has a compression of 0.045m. The spring is then released to launch the ball. The kinetic energy of the ball as it leaves the toy is 0.72 J. The ball in (b) leaves the toy at point A and moves vertically upwards through the air. Point B is the position of the ball when it is at maximum height h above point A, as illustrated in Fig. 3.2. [Figure 3.2] The gravitational potential energy of the ball increases by 0.60 J as it moves from A to B.