Un bloque con masa igual 1.00 Kg se lanza sobre una superficie horizontal de madera con una rapidez inicial de 4.0 m/s. Debido a la fuerza de ficción por deslizamiento el
bloque se detiene después de haber recorrido 15.0 m. Determine:
a) La aceleración del movimiento.
b) El coeficiente de fricción cinético.
c) El tiempo que dura el bloque en movimiento

a) a = 0.533 [m/s²]

b) μ  = 0.0543

c) t = 7.5 [s]

Explanation:

Para poder solucionar este problema, ya que nos dan la masa y la velocidad del cuerpo podemos encontrar la energia cinetica, como tambien nos dan una distancia de recorrido, esta se relaciona con el trabajo. De esta manera la primera pista para resolver el problema es utilizando el teorema de la conservacion de la energia y el trabajo. Vamos a suponer que el bloque se lanza hacia la derecha (hacia la derecha el movimiento es positivo).

En la anterior ecuacion nos dice que la energia en el punto final 2, es igual a la suma de la energia en el punto nicial (1) mas la suma de trabajo realizado sobre el bloque de madera.

La energia inicial (1), corresponde a la energia cinetica = E₁ = 0.5*m*v₁²

Donde:

m = masa = 1 [kg]

v₁ = velocidad inicial = 4 [m/s]

La energia inicial (2), corresponde a la energia cinetica = E₂ = 0.5*m*v₂²

Donde:

m = masa = 1 [kg]

v₂ = velocidad final = 0 (el bloque se detiene)

El trabajo W₁₋₂ se define como el producto de la fuerza por la distancia, como la unica fuerza que se opone al movimiento es la friccion, esta actua en sentido opuesto al movimiento. Por ende llevara signo negativo.

W₁₋₂ = - f*d = -f*15

Ahora reemplazando tenemos:

0.5*m*v₁² - 15*f  = 0.5*m*v₂²

0.5*1*(4)² - 15*f = 0.5*1*(0)²

0.5*1*(4)² = 15*f

f = 0.533 [N]

a) Utilizando la segunda ley de Newton la cual nos dice que la sumatoria de fuerzas es igual al producto de la masa por la aceleracion, entonces tenemos:

ΣF =m*a

Como la unica fuerza que tenemos es la friccion, reemplazamos y podemos encontrar la aceleracion.

f = m*a

0.533 = 1*a

a = 0.533 [m/s²]

b) La fuerza de friccion se define como el producto de la fuerza normal por el coeficiente de friccion:

f = μ*N

Donde:

μ = coeficiente de friccion

N = Fuerza normal [N]

Y la fuerza normal N se define como la reaccion al peso (siempre y cuando el bloque o el cuerpo se encuentre sobre una superficie horizontal, si se encuentra en una superficie inclinada se recomienda realizar un diagrama de cuerpo libre)

N = m*g = 1*9.81 = 9.81[N]

μ = f/N

μ  = 0.533/9.81

μ  = 0.0543

c)

Para poder encontrar dicho tiempo debemos de utilizar la siguiente ecuacion de la cinematica.

V = Vo - (a*t)

donde:

V = velocidad final = 0

Vo = velocidad inicial = 4 [m/s]

a = aceleracion =  0.533 [m/s²]

t = tiempo [s]

Nota: El signo negativo en la anterior ecuacion significa que el bloque o cuerpo se desacelera o pierde velocidad hasta detenerse.

0 = 4 - 0.533*t

t = 4/0.533

t = 7.5 [s]

relativism, roughly put, is the view that truth and falsity, right and wrong, standards of reasoning, and procedures of justification are products of differing conventions and frameworks of assessment and that their authority is confined to the context giving rise to them. more precisely, “relativism” covers views which maintain that—at a high level of abstraction—at least some class of things have the properties they have (e.g., beautiful, morally good, epistemically justified) not simpliciter, but only relative to a given framework of assessment (e.g., local cultural norms, individual standards), and correspondingly, that the truth of claims attributing these properties holds only once the relevant framework of assessment is specified or supplied. relativists characteristically insist, furthermore, that if something is only relatively so, then there can be no framework-independent vantage point from which the matter of whether the thing in question is so can be established.

relativism has been, in its various guises, both one of the most popular and most reviled philosophical doctrines of our time. defenders see it as a harbinger of tolerance and the only ethical and epistemic stance worthy of the open-minded and tolerant. detractors dismiss it for its alleged incoherence and uncritical intellectual permissiveness. debates about relativism permeate the whole spectrum of philosophical sub-disciplines. from ethics to epistemology, science to religion, political theory to ontology, theories of meaning and even logic, philosophy has felt the need to respond to this heady and seemingly subversive idea. discussions of relativism often also invoke considerations relevant to the very nature and methodology of philosophy and to the division between the so-called “analytic and continental” camps in philosophy. and yet, despite a long history of debate going back to plato and an increasingly large body of writing, it is still difficult to come to an agreed definition of what, at its core, relativism is, and what philosophical import it has. this entry attempts to provide a broad account of the many ways in which “relativism” has been defined, explained, defended and criticized.

explanation:

"i have always loved contemporary art and made it a general goal to work within the field. after a few nonprofit internships at museums and galleries, i decided to try the for-profit art world and was offered a job as the ad assistant at the magazine. i much prefer the pace of the for-profit art community and have stayed with the company for three years, with a promotion to an account manager last spring."

i just did this and got a 100.