Answer:
c) 10.7m/s
Explanation:
From the exercise we know that at 5m the ball is traveling at 4m/s
To calculate its initial velocity we need to solve the following equation:

Since the initial height is 0
Solving for 

Answer:
λ = hv
If frequency is doubled :
λ = h × 2v
λ = 2hv
Thus wavelength is doubled
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