calculate the change in thermal energy when 120kg of sand warms from 10 degrees celcius to 90 degrees celcius

Answer 1

Look up the specific heat of sand. Call it C.

http://apollo.lsc.vsc.edu/classes/met130/notes/chapter2/spec_heats.html
has some values

The thermal energy increase is
deltaU = Q = M*C*(deltaT)
where deltaT = 80 C