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Awesome! The ball returns to its initial position. So, both the initial and final positions are $$y=10$$. Therefore, the displacement is $$10-10=0$$.
We talked about speed earlier. Let's introduce a related concept called velocity. You will use velocity throughout Physics. So, it is important that you understand its meaning thoroughly! Velocity is just the rate of change of displacement.

So, to calculate velocity, calculate the displacement and divide it by the time taken. $$\text{Velocity} = \frac{\text{Displacement}}{\text{Time}}$$. In calculus terms, $$v = \frac{dr}{dt}$$, where $$v$$ is the velocity, $$r$$ is the position and $$t$$ is the time.
If the ball takes $$5 \, \mathrm{s}$$ to return, which is correct?
• $$\mathrm{Velocity} \, = 4 \, \mathrm{m/s}$$, $$\mathrm{Speed} \, = 4 \mathrm{m/s}$$
• $$\mathrm{Velocity} \, = 0 \, \mathrm{m/s}$$, $$\mathrm{Speed} \, = 4 \mathrm{m/s}$$
• $$\mathrm{Velocity} \, = 4 \, \mathrm{m/s}$$, $$\mathrm{Speed} \, = 0 \mathrm{m/s}$$
• $$\mathrm{Velocity} \, = 0 \, \mathrm{m/s}$$, $$\mathrm{Speed} \, = 0 \mathrm{m/s}$$