A dolphin is swimming under water at a constant speed of 4.50ms⁻¹.

1. (a)The dolphin emits a sound as it swims directly towards a stationary submerged diver. The frequency of the sound heard by the diver is 9560Hz. The speed of sound in the water is 1510ms⁻¹. Determine the frequency, to three significant figures, of the sound emitted by the dolphin.[2]
2. (b)(i)The dolphin strikes the bottom of a floating ball so that the ball rises vertically upwards from the surface of the water, as illustrated in Fig. 2.1. [Figure 2.1] The ball leaves the water surface with speed 5.6ms⁻¹. Assume that air resistance is negligible. Calculate the maximum height reached by the ball above the surface of the water.[2]
3. (b)(ii)The ball leaves the water at time t = 0 and reaches its maximum height at time t = T. On Fig. 2.2, sketch a graph to show the variation of the speed of the ball with time t from t = 0 to t = T. Numerical values are not required. [Figure 2.2][1]
4. (b)(iii)The mass of the ball is 0.45 kg. Use your answer in (b)(i) to calculate the change in gravitational potential energy of the ball as it rises from the surface of the water to its maximum height.[2]
5. (b)(iv)State and explain the variation in the magnitude of the acceleration of the ball as it falls back towards the surface of the water if air resistance is not negligible.[2]

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