Answer:
T = 13.3 N
Explanation:
In this exercise we use Newton's second law, in the lower birth of the circle the tension and force are opposite, so the tension has its maximum value
T - W = m a
The acceleration is centripetal
a = v² / r = w² r
We replace
T = mg + m w² r
The angular velocity is related to the period
w = 2π f = 2π / T₀
T₀ = 2.10 s
T = m (g + 4π² r / T₀²)
Let's calculate
T = 1.35 (9.8 + 4π² 1.10 /2.10²)
T = 13.3 N
Answer:
t = 9.16 10⁻⁸ m
Explanation:
In this exercise we fear a case of interference by reflection,
We have two aspects
* when the light ray passes from the air to the TiO2 that has a higher refraction start, the reflected ray has a phase change of 180º
* when the beam is inside the material its wavelength changes
λₙ = λ₀ / n
with these two done the equation for destructive interference remains
2t = m λₙ
2nt = m λ₀
They ask us for the thickness t of the film for m = 1
t = m λ₀ / 2n
let's calculate
t = 
t = 9.16 10⁻⁸ m
By Newton's second law, the net vertical force acting on the object is 0, so that
<em>n</em> - <em>w</em> = 0
where <em>n</em> = magnitude of the normal force of the surface pushing up on the object, and <em>w</em> = weight of the object. Hence <em>n</em> = <em>w</em> = <em>mg</em> = 196 N, where <em>m</em> = 20 kg and <em>g</em> = 9.80 m/s².
The force of static friction exerts up to 80 N on the object, since that's the minimum required force needed to get it moving, which means the coefficient of <u>static</u> friction <em>µ</em> is such that
80 N = <em>µ</em> (196 N) → <em>µ</em> = (80 N)/(196 N) ≈ 0.408
Moving at constant speed, there is a kinetic friction force of 40 N opposing the object's motion, so that the coefficient of <u>kinetic</u> friction <em>ν</em> is
40 N = <em>ν</em> (196 N) → <em>ν</em> = (40 N)/(196 N) ≈ 0.204
And so the closest answer is C.
(Note: <em>µ</em> and <em>ν</em> are the Greek letters mu and nu)
