In an isolated system where two blocks of different temperatures are in thermal contact, heat will flow from the hotter object to the cooler one until they reach thermal equilibrium. In this case, Block 1 starts at 40 degrees Celsius and Block 2 starts at 20 degrees Celsius.
The final temperature of both blocks, once they reach equilibrium, will be somewhere between 20 degrees Celsius and 40 degrees Celsius. The exact final temperature can be calculated using the concept of heat transfer, taking into account their respective masses and specific heat capacities. If we assume both blocks have the same mass and specific heat capacities, the final temperature \( T_f \) can be calculated as:
\[ T_f = \frac{(m_1 \cdot T_1 + m_2 \cdot T_2)}{m_1 + m_2} \]
Assuming equal masses for simplification:
\[ T_f = \frac{(1 \cdot 40 + 1 \cdot 20)}{1 + 1} = \frac{60}{2} = 30 \text{ degrees Celsius} \]
Thus, the ending temperature of both blocks will be 30 degrees Celsius.
If you have pictures to choose from, the correct picture would be one showing both blocks at 30 degrees Celsius.