The robertson-walker metric is given by dr2 d. s2 -dt a(t) 1kr r(d02 + sin2 odo (iii the parameter k corresponds to the square of the inverse-radius of curvature. discuss the physical significance of: positive spatial curvature, i. e. k > 0; and negative spatial curvature, i. e. k < 0, with respect to the extent of the universe and the behaviour of parallel geodesics (iv) it is believed that our universe has approximately zero spatial curvature, i. e. k = 0. given this, write down an expression for the speed of radially propagating light in terms of the robertson-walker co-ordinates (v) given that a(t) is increasing with time, what does this light speed imply about the frequency of light observed from distant galaxies? to answer this question consider how long it takes for light to propagate a fixed co-ordinate distance dr in the present, and the same fixed co-ordinate distance at some time in the past. you can relate the time intervals obtained st*, to frequencies via w; 2n/dt; .

a longitudinal wave moves energy that is to the direction of the wave’s movement. - true

which piece of furniture will have the most inertia and give the furniture movers the most difficulty in moving?  

answer

a 75kg dining table

russian is not my first language, so i'm afraid i can't write out an answer in russian, but hopefully you can find a way to do so. here's my best translation of the problem: you're given a plot of a particle's position in one-dimensional space over time, and you're asked to find either the total distance traveled by the particle after 6 seconds had elapsed, or the total displacement of the particle after 6 seconds.

if you want the total distance traveled, you would first need to determine the particle's velocity as a function of time, then integrate that over the 6-second interval. we know the position function is quadratic with roots at 0 and 6, so we have

where is unknown. because the position is parabolic, there is symmetry about the midpoint at , and we know that

so that the position function is

which means the velocity is

then the total distance traveled is

so the total distance traveled is 20 m.

on the other hand, if you want to find displacement: the particle starts at and ends at , so its displacement is 0.