What is the Jeans instability?

A When a growing protoplanet becomes too large, it is more likely to be split apart by subsequent bombardment than to grow further.

B If a solar nebula is too massive it will continue to collapse to become a black hole and will not form planets.

C If the disk of matter surrounding a solar nebula becomes too hot, it will dissipate, and planets will not form.

D If a cloud of gas and dust is sufficiently dense, it will collapse due to its own gravity.

Space-time metric ds2= -dt2+at2dx2+bt2dy2+ct2dz2 (a)how does the area of a rectangle with vertices at ( x=0, y=0, z=0 ), (1,0,0 ), ( 0,1,0 ) and (1,1,0 ) changes with time? (b) if a photon moving in the x direction starts from the origin at t=1, when does it reach x=l? (ds=0 for the trajectory of a photon.) (c) the proper time for a particle is defined by cd=ds. what is the proper time for a particle to move along the trajectory ( x(t)=t, y(t)=0, z(t)=0 ) from t=0 to 1 ? what is the condition on the parameter a so that the velocity of the particle never exceeds the speed of light ?

Waves that cause the most damage during an earthquake are a. surface waves c. s waves b. p waves d. ocean waves

What are the starting materials for nuclear fission? two small nuclei two large nuclei a neutron and a large nucleus a neutron and a small nucleus