# Energy (heat?)

1. Dec 15, 2006

### BunDa4Th

1. The problem statement, all variables and given/known data

Suppose a steel strut with cross-sectional area 7.00x10^-4 m2 and length 2.50 m is bolted between two rigid bulkheads in the engine room of a submarine.
(a) Calculate the change in temperature of the strut if it absorbs an energy of 3.00x10^5 J. °C

2. Relevant equations

Q = mcDeltaT
DeltaT = Q/mc

3. The attempt at a solution

I tried using the formula DeltaT = Q/mc

Delta T = 3.00 x 10^5/ m(448 J/kg *C)

the problem im having is how do i find the mass?

2. Dec 15, 2006

### andrevdh

Density of steel $$\rho _{steel} = 7.8 \times 10^3\ kg/m^3$$

3. Dec 15, 2006

### BunDa4Th

I still dont understand how to solve this problem knowing the density of steel.

4. Dec 15, 2006

### Staff: Mentor

Use it to find the mass of the steel.

5. Dec 15, 2006

### BunDa4Th

m = psteelV

how do i find v?

Last edited: Dec 15, 2006
6. Dec 15, 2006

### cristo

Staff Emeritus
No. You are given the cross sectional area and the length. Do you know how to calculate the volume from this information?

7. Dec 15, 2006

### BunDa4Th

okay i figure out how to solve this.

it was P_steel x cross sec. area / length = m

8. Dec 15, 2006

### cristo

Staff Emeritus
Not quite: V=A*l (where A is the cross sec. area, l is the length). Above you had the correct forumla: m= ρ*V and so m= ρ*A*l

9. Dec 15, 2006

### BunDa4Th

oops, my mistake. yes i did mean m = p x A x l that was how i got the correct answer.

Thanks for the correction and help.