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1 answer:
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Answer:
987 joules, 3.01s
Explanation:
(A)
from the attached diagram
net force, Fnet, pulling the crate up the ramp is given by
Fnet = FcosФ - WsinФ - Fr
where FcosФ is the component of horizontal force 290N resolved parallel to the plane
WsinФ = mgsinФ = component of the weight of the crate resolved parallel to the plane
Fr = constant opposing frictional force
Fnet = 290cos34⁰ - 20 × 9.8 × sin34° - 65
Fnet = 240.421 - 109.602 - 65
Fnet = 65.82N
Work done on the crate up the ramp, W, is given by
W = Fnet × d (distance up the plane)
W = 65.819 × 15
W = 987.285 joules
W = 987 joules (to 3 significant Figures)
(B)
to calculate the time of travel up the ramp
we use the equation of motion
where s = distance up the plane, 15m
u = Initial velocity of the crate, which is 0 for a body that is initially at rest
a = acceleration up the plane, given by
where m = mass of the crate, 20 kg
now,
from,
15 = 0 + 1.645
15 = 1.645
t = 3.01s (to 3 sig fig)
C. A could be ruby (speed of light = 170,000 km/s); B could be diamond (speed of light = 120,000 km/s).
Explanation:
Refraction is a phenomenon that occurs when a light rays crosses the boundary between two different mediums.
When this occurs, the light wave changes speed and also direction, according to Snell's law:
(1)
where
is the index of refraction of the first medium
is the index of refraction of the second medium
is the angle of incidence (the angle between the incident ray and the normal to the boundary)
is the angle of refraction (the angle between the refracted ray and the normal to the boundary)
The index of refraction is the ratio between the speed of light in a vacuum (c) and the speed of light in the medium (v):
Using this definition, we can rewrite eq.(1) as
Where is the speed of light in the 2nd medium and
the speed of light in the 1st medium.
Now let's analyze the situation represented in the figure: we see that as the light ray enters the 2nd medium, it bends towards the normal, this means that the angle of refraction is smaller than the angle of incidence:
This means that
And therefore,
So, the speed of light in the second medium is smaller than the speed of light in the first medium: this occurs only in option C), which is therefore the correct choice.
Learn more about refraction:
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