Answer:
7800 J 
Step-by-step explanation:
Heat needed = mass of copper x specific heat of copper x change in temperature 
Change in temperature = 30ºC - 20ºC = 10ºC 
Specific heat of copper = 390 J/kgºC 
Mass of copper = 2 Kg 
Substituting the given values in above equation, we get – 
 
Heat needed = 2 Kg x 390 J/kgºC x 10ºC 
= 7800 J