[sozan]

احتاج لمساعدة عاجلة ..
هذه هي اولى مشاركاتي في منتداكم .. وانا أتأمل ان اجد لي بينكم مكانا ..
انا طالبة جامعية , سنة اولى فيزياء وانا لم ادرس من قبل موضوع الفيزياء وعندي مجموعة من الاسئلة مع مقترحات حلول لها كنت قد جربتها ولكن اجابتي كانت خاطئة .. اريد منكم ان تساعدوني في حلها ..

السؤال الأول :
[align=left]A pendulum has a length L = 1.00 m. It hangs straight down in a jet plane about to take off as shown by the dotted line in the figure.

http://uae4up.com/uploads/cb6c6cf3dd.gif

The jet accelerates uniformly, and during that time, the pendulum oscillates about the equilibrium position shown by the solid line, with D = 0.400 m. Calculate the magnitude of the plane's acceleration.[/align]

مقترح الحل :

[align=left] If the pendulum were stationary, its acceleration at this point would perpendicular to L and be given as:
sin(theta) = D/L
sin(theta) = 0.4/1
theta = 23.58 deg

a = g*sin(theta)
a = 9.8*0.4
a = 3.92

The to keep the equilibrium point here, the jet's acceleration must be equal to the x component of this acceleration:
a_x = a*cos(theta)
a_x = 3.92*cos(23.58)
a_x = 3.59 m/sec^2 [/align]

لكن الاجابة خاطئة ولا اعلم لماذا ؟؟!!

........................................

السؤال الثاني :

[align=left]part1:
A 29.0 kg block at rest on a horizontal frictionless air track is connected to the wall via a spring. The equilibrium position of the mass is defined to be at x=0. Somebody pushes the mass to the position x= 0.350 m, then lets go. The mass undergoes simple harmonic motion with a period of 4.50 s. What is the position of the mass 3.600 s after the mass is released?

part2:
Consider the same mass and spring discussed in the previous problem. What is the magnitude of the maximum acceleration the mass undergoes during its motion?[/align]


مقترح الحل :
[align=left]I found the angular velocity by using
\omega = 2\pi/ T and got it to be 1.795. I then plugged it into the equation, a= -\omega^2 x_{m}cos(\omega t +\theta)
with x= .206 m, and t=2.975 s. I got a= .389 m/S^2, which isn't right. [/align]

يا ريت شي حدا يساعدني .. عندي كمان اسئلة بس حاليا بكتفي بهذه الاسئلة ...
شكرا مسبقا ..

[sozan]

this is the figure of question 2 :

http://www3.0zz0.com/2006/12/22/10/61592534.jpg

[sozan]

اين الرد يا جماعة ؟؟
احتاج للمساعدة باسرع وقت ممكن ..