Thermodynamics - Change in temperature for heated slabs of steel

[CJoy]

Homework Statement

Defiance Drake, Space Adventurer, has managed to lay claim to an abandoned freighter whose crew was killed by Cubarb parasites. She fired the engines of her craft for 30 seconds, which involved igniting unobtainium gas to propel the ship (in an action-reaction process). During this time, the engine cones absorbed some of the heat of this explosion. If one can approximate the engine cones as four slabs of 700 kg steel, 70000 kJ of heat was absorbed, and the initial temperature of the steel was -250 Celsius, what is the final temperature? Is the steel in danger of melting?

Relevant Equations

mass of object x change in temp x specific heat capacity= heat

Just started this topic so I'm not sure if this is the correct way to solve this, any help would be appreciated.
mass of object x change in temp x specific heat capacity= heat
change in temp= heat/(mass of object x specific heat capacity)
Mass= 700kg
Specific heat capacity of steel= 0.42kJ/kgC
heat=70000kJ
change in temp= temp final- temp initial
temp initial=-250C
change in temp= (70000)/(700 x 0.42)=238.095C
Temp final - temp initial= 238.095C
Temp final - (-250C)=238.095C
Temp final= 488.095C
Since steel's melting point is at 1370C, the steel is not in danger of melting.

 

[mfig]

That procedure looks good, except I wonder if the total mass is 4x what you have used. Is it 4 slabs of 700 kg each or 4 slabs with a combined mass of 700 kg? Seems like the problem wouldn't mention the number of slabs if it gave the total mass.

 

[Andrew Mason]

change in temp= temp final- temp initial
temp initial=-250C
change in temp= (70000)/(700 x 0.42)=238.095C
Temp final - temp initial= 238.095C
Temp final - (-250C)=238.095C
Temp final= 488.095C
Since steel's melting point is at 1370C, the steel is not in danger of melting.

Hi Cjoy. Better check your algebra. If you started at -250C and the change was 238C it will be below 0 C.

AM

 

[CJoy]

With the changes, does this look correct?
Mass= 700kg x 4=2800kg
Specific heat capacity of steel= 0.42kJ/kgC
heat=70000kJ
change in temp= temp final- temp initial
temp initial=-250C
change in temp= (70000)/(2800 x 0.42)=59.5C
Temp final - temp initial= 59.5C
Temp final - (-250C)=59.5C
Temp final= -190.476C