The variation with extension x of the force Facting on a spring is shown in Fig. 3.1. [Figure 3.1] The spring of unstretched length 0.40 m has one end attached to a fixed point, as shown in Fig. 3.2. [Figure 3.2] A block of weight 2.5 N is then attached to the spring. The block is then released and begins to move downwards. At one instant, as the block is continuing to move downwards, the spring has a length of 0.72 m, as shown in Fig. 3.3. [Figure 3.3] Assume that the air resistance and the mass of the spring are both negligible.

1. (a)For the change in length of the spring from 0.40 m to 0.72 m:
2. (a)(i)use Fig. 3.1 to show that the increase in elastic potential energy of the spring is 0.64 J[2]
3. (a)(ii)calculate the decrease in gravitational potential energy of the block of weight 2.5 N.[2]
4. (b)Use the information in (a)(i) and your answer in (a)(ii) to determine, for the instant when the length of the spring is 0.72 m:
5. (b)(i)the kinetic energy of the block[1]
6. (b)(ii)the speed of the block.[2]

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