The answer is C, because it hits a dense medium, which causes it to bounce off.
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Answer:

Explanation:
From the question we are told that:
Time 
Generally the Period is given as

Therefore difference in frequency dF



Answer:
15 N and 3.061
Explanation:
From the question,
The minimum force of friction to keep the book from sliding = 15 N.
using
F = mgμ................. Equation 1
Where F = Frictional Force, m = mass of the book, g = acceleration due to gravity, μ = coefficient of friction.
make μ the subject of the equation
μ = F/mg............... Equation 2
Given: F = 15 N, m = 0.5 kg, g = 9.8 m/s²
Substitute into equation 2
μ = 15(0.5×9.8)
μ = 15/4.9
μ = 3.061
Hence the coefficient of friction to keep the book from sliding = 3.061
Answer:
constant horizontal force developed in the coupling C = 11.25KN
the friction force developed between the tires of the truck and the road during this time is 33.75KN
Explanation:
See attached file