A dolphin sends out a sound while heading straight towards a stationary diver underwater. The diver hears the sound at $9560\,\text{Hz}$. The speed of sound in water is $1510\,\text{m s}^{-1}$. Find, to three significant figures, the frequency emitted by the dolphin.
The dolphin pushes on the bottom of a floating ball so that the ball moves straight upward from the water surface, as shown in Fig. 2.1. It leaves the surface with speed $5.6\,\text{m s}^{-1}$. Ignore air resistance.
Calculate the greatest height reached by the ball above the water surface.
The ball leaves the water at $t = 0$ and reaches its greatest height at $t = T$. On Fig. 2.2, sketch how the ball’s speed varies with time $t$ from $t = 0$ to $t = T$. No numerical values are needed.
The mass of the ball is $0.45\,\text{kg}$. Using your value from (b)(i), calculate the change in gravitational potential energy of the ball as it rises from the water surface to its highest point.
State and explain how the magnitude of the ball’s acceleration changes as it returns towards the water surface if air resistance cannot be ignored.