Question

As the solar nebula shrank it became hotter because......

1) Its gravitational potential energy was converted to kinetic energy and then into thermal energy.
2) Radiation from other nearby stars that had formed earlier heated the nebula.
3) Nuclear fusion occurring in the core of the protosun produced energy that heated the nebula.
4) The shock wave from a nearby supernova heated the gas.
5) Collisions among planetesimals generated friction and heat.

Answer 1

The solar nebula became hotter as it shrank because its gravitational potential energy was converted to kinetic energy and then into thermal energy. The material in the center formed a star, which produced its own energy to maintain high temperatures in its immediate neighborhood.

Step-by-step explanation:

The solar nebula became hotter as it shrank because its gravitational potential energy was converted to kinetic energy and then into thermal energy. As the gas particles in the nebula raced toward the center due to gravitational attraction, their kinetic energy transferred into thermal energy through collisions, generating a hot ball of gas that would become a star. The material in the center of the nebula formed a star, which maintained high temperatures in its immediate neighborhood by producing its own energy.