Question

Steel blocks A and B, which have equal masses, are at TA = 300 oC and T8 = 400 oC. Block C, with mc - 2mA, is at TC = 350 oC. Blocks A and B are placed in contact, isolated, and allowed to come into equilibrium. Then they are placed in contact with block C. At that instant:a.TA = TB < TCb.TA = TB = TCc.TA = TB > TCd.TA + TB = TCe.TA - TB = TC

Answer 1

Answer:

b) TA = TB = TC

Explanation:

• When put in contact each other, and isolated, both blocks will exchange heat till they reach to thermal equilibrium.
• During this process, the body at a higher temperature, will loss heat, tat it will be gained by the other body.
• The equilibrium condition will be reached when the following equation be met:

       $\Delta Q = c_{st}* m_{A} * (T_{fin} - T_{0A} ) = c_{st}* m_{B} * (T_{0B} - T_{fin} )$

• Replacing by the values of T₀A = 300º C, and T₀B = 400ºC, and simplifying common terms as mA = mB, we can solve for  Tfin, as follows:

       $(400 \ºC - T_{fin}) = (T_{fin} - 300 \ºC) \\ \\ 2* T_{fin} = 700\ºC\\ \\ T_{fin} = 350\ºC$

• So, when both blocks reach to equilibrium, they will be at a common final temperature, 350ºC.
• When put in contact with block C, at the same temperature, at that instant, the three blocks will have the same common temperature of 350 ºC.
• So, option b) is the right one.