Astellar core of mass 3.0 x 10^30 kg and radius 4.0 x 10^8 m collapses, with no loss of mass, to become a neutron star with radius 7.5 x 10^3 m. what is the change in gravitational potential energy of 1.0 × 10^3 kg of material that was initially at the surface of the stellar core and that ends up at the surface of the neutron star?

Awater balloon launcher uses an elastic band with a spring constant of 115 n/m to use thee launcher you stretch thee band back with a balloon n it the water balloons have a mass of 1.3 kg a) if you stretch the band by 0.8 m, what elastic force will the band exert? b) with the band stretched 0.8 m, how much elastic potential energy is stored in the spring? c) if you release the band, it pushes forward. what is the kinetic energy of the balloon when it reaches the natural length of the band? d) what is the speed of the balloon when it reaches the natural length of the band?