The wavelength

of the wave is 160 m, and this is the distance between two consecutive crests. The boat is located at a crest of the wave, this means that the first trough is located 80 meters from the boat (because the distance between a crest and a trough is half the wavelength).
The speed of the wave is

so the time the boat takes to reach the first trough is
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Answer:
90 m
Explanation:
Acceleration,
where v and u are final and initial velocities respectively, t is the time taken
Substituting
for a, 4 m/s for u and 10 s for t then
1*10=v-4
v=14 m/s
From kinematic equations

Making s the subject then

Answer
given,
diameter of sphere = 5 cm
radius of sphere = -2.5 cm
refractive index for glass n₁ = 1.5
refractive index for air n₂ = 1
magnification of the glass = ?
now,



S' = - 10 cm
magnification


m = + 3