物理讨论专区

Log

回复 440# Winterblade
amplitude= (  f1² - f2² )/8
simplify, u obtain  y=  ( f1² - f2² )/8 . sin  4(pi)t

vick5821

so the stationary wave equation is actually for the particlar wave de?? and if we wan to calculate for the displacement of particular element at particular distance, we sub nto cos kx?? how bout the time??

vick5821

2cos x = amplitude then y is what??

Log

yes stationary wave equation
when find color=Red]max  displacement, we can sub into the cos kx
when we want to find a particular displacement of a element at a particular distance at time t, we just insert all the info into the equation.  
2cos x = amplitude then y is what??
that it is just an example so  dun bother it but
if this is wave equation, then  y is displacement of the particle at time t

jennykuwn

我有一题physic 问题， 请各位大大帮帮忙。。
The distance of the Earth from the Sun is 1.5 x 10^11 m. The mass of the Sun is (3.24 x 10^5)M where M is the mass of the Earth.
Find the distance from the Earth along the line joining the Earth to the Sun where the gravitational attraction of the Sun is equal that of the Earth.

Log

回复 445# jennykuwn
assume a body mass m is situated between earth and sun
distance between earth and mass=r
distance between sun and mass = 1.5 x 10^11 - r
  force earth = force sun
use F=GMm/r^2
GMm/r^2 = G(3.24 x 10^5 M)m / (1.5 x 10^11 - r)^2
1/r^2 = (3.24 x 10^5 )/ (1.5 x 10^11 - r)^2
solve, using quadratic formula,  u will get the r.
r=2.63 x 10^8 m

vick5821

I still cant differentiate between the two..y= cos kx sin wt, the y is calculate for what and the cos kx is what?

vick5821

Two sound waves with frequencies 450Hz and 458Hz undergo superposition. Calculate the
i) frequency of the resultant wave
ii) beat

how to calculate ar???haiz..dun understand..dun quite understand actually about beat

Log

1.y is displacement of particle at time t, cos kx is amplitude ,  always remember amplitude depends on the fixed x.

for Q 2,
resultant wave frequency = (f1+f2)/2
beat frequency=f1-f2
beat frequency mean no of beats u heard in 1 s time
resultant frequency is the no of complete oscillations made by the two waves in 1 s

vick5821

then calculate maximum displacement why you use cos kx?? isnt that y= ___?

vick5821

amplitude is maximum displacement..it does not depends on t meh?? the y does not depends on x?

Log

yes, calculate displacement we use y =cos kx sin wt
but y is MAX displacement  when  at sin wt =1
so, max displacement= cos kx
y is depends on t ,amplitude depends on  x , x is fixed

vick5821

Can give me some others example questions??

vick5821

y calculate the displacement of what?? particle on the wave? or the wave?

vick5821

One ques here

A transverse sinusoidal wave on a string has a period T= 25.0 ms and travels in the negative x direction with a speed of 30.0 ms -1. At t=0 s, a particle on the string at x = 0m has a trasverse position of 2.0m and is travelling downwards with a speed of 2.0 ms-1. Calculate the amplitude, maximum speed of particle and wavelength..

I dun understand why they give the particle's velocity..use for what?

vick5821

One ques here

A transverse sinusoidal wave on a string has a period T= 25.0 ms and travels in the negative x direction with a speed of 30.0 ms -1. At t=0 s, a particle on the string at x = 0m has a trasverse position of 2.0m and is travelling downwards with a speed of 2.0 ms-1. Calculate the amplitude, maximum speed of particle and wavelength..

I dun understand why they give the particle's velocity..use for what?

Winterblade

回复 456# vick5821


    You got the answers?

vick5821

Yes...我有答案

vick5821

At what point on a stationary waves that maximum sound is heard, the node or antinode?

Winterblade

回复 458# vick5821


    oo please give me